Bug: StreamdownRN causes jumpy scroll behavior in FlashList v2 (Expo 54, new arch)

[eliasljubec]

Janky/jumpy scrolling behavior with StreamdownRN in FlashList v2 (Expo 54 + New Architecture)

First off, really appreciate the work on StreamdownRN, it's awesome ❤️. The streaming markdown capabilities are really nice!

Description

When rendering markdown content with StreamdownRN inside a FlashList v2 component, scrolling upward causes janky and jumpy behavior. This seems specific to the initial rendering of StreamdownRN components, as scrolling downward after the list has been rendered works correctly.

Environment

• Expo SDK: 54.0.25
• React Native: 0.81.5
• FlashList: 2.0.2
• StreamdownRN: 0.1.6
• Architecture: New Architecture enabled
• Platform: tested on iOS device only

Note: This issue was not present with Expo 53 and FlashList v1.

Steps to Reproduce

1. Hook up the minimal example provided below.
2. Scroll upward and try to count all 6 images in the list.
   • With StreamdownRN, you won’t be able to count all 6 due to the jumpy behavior. See: Screen Recording
   • With Markdown from react-native-markdown-display (which StreamdownRN uses under the hood) directly, all 6 images are shown and countable when scrolling up. See: Screen Recording

Minimal Reproducible Example

Minimal example file:

chat-history.tsx

Expected Behavior

Smooth scrolling in both directions, with all list items visible and accessible when scrolling upward.

Actual Behavior

• Scrolling upward: Initially janky, jumpy behavior. Some items may not be visible or accessible (e.g. when counting images, not all 6 images can be counted when scrolling up).
• Scrolling downward: Works correctly after initial render.
• With react-native-markdown-display directly: Scrolling works fine.

[edgarpavlovsky]

hey @eliasljubec - appreciate the kind words! we just did a major refactor and package should be more stable, but i didn't get to debug this behavior. could you try with the latest and lmk if you're seeing the same thing?

[eliasljubec]

Hi @edgarpavlovsky - thanks for the reply,

I tested again with the latest version. Previously it was skipping/jumping messages, but now messages get also mixed up and occasionally jump around when scrolling. I’ve added two screen recordings. In the videos I’m just trying to scroll up from message 20 to message 1, and you can see the odd behaviour.

I’ve rendered the index inside each message so you can see that, when using StreamdownRN, the messages do not appear in chronological order while scrolling, messages show the wrong index/appear out of sequence. For comparison, with react-native-markdown-display directly, the same list scrolls as expected and the indexes remain in the correct chronological order.

• Screen recording using StreamdownRN: recording
• Screen recording using react-native-markdown-display: recording

To reproduce this, hook up the example I’m using to showcase the issue:

chat-history-v2.tsx

[edgarpavlovsky]

@eliasljubec i tried to reproduce with LegendList and wasn't seeing the same behavior, added chat history to the debugger-ios app: #13

[eliasljubec]

Did you get a chance to run the example I provided? It’s a minimal setup that reproduces the issue with FlashList v2.

I also tried it with LegendList, it behaves better, but when you set initialScrollIndex to the most recent message and then scroll from message 20 up to message 1, you can still see the jumping on the initial scroll up. It’s subtle with LegendList and much more obvious with FlashList v2.

These are just the observations we’ve made so far - it could also be a new architecture quirk thingy, not sure.. since we started seeing this after migrating from expo 53 to 54 with the new arch enabled.

[edgarpavlovsky]

Taking my time on this so that I can test your experience - will try to revert soon Sent via Superhuman ( ***@***.*** )

…

On Thu, Dec 04, 2025 at 4:49 PM, Elias Ljubec < ***@***.*** > wrote: *eliasljubec* left a comment (darkresearch/ generative-ui#9) ( #9 (comment) ) Did you get a chance to run the example I provided? It’s a minimal setup that reproduces the issue with FlashList v2. I also tried it with LegendList, it behaves better, but when you set initialScrollIndex to the most recent message and then scroll from message 20 up to message 1, you can still see the jumping on the initial scroll up. It’s subtle with LegendList and much more obvious with FlashList v2. These are just the observations we’ve made so far - it could also be a new architecture quirk thingy, not sure.. since we started seeing this after migrating from expo 53 to 54 with the new arch enabled. — Reply to this email directly, view it on GitHub ( #9 (comment) ) , or unsubscribe ( https://github.com/notifications/unsubscribe-auth/AC32YXRPSVEBOT2JNIPJ2CD4AAUTZAVCNFSM6AAAAACNZYMXXSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMMJSGA4TMMJSGE ). You are receiving this because you were mentioned. Message ID: <darkresearch/generative-ui/issues/9/3612096121 @ github. com>

[joaoterrantez04-ctrl]

Hi @edgarpavlovsky - thanks for the reply,

I tested again with the latest version. Previously it was skipping/jumping messages, but now messages get also mixed up and occasionally jump around when scrolling. I’ve added two screen recordings. In the videos I’m just trying to scroll up from message 20 to message 1, and you can see the odd behaviour.

I’ve rendered the index inside each message so you can see that, when using StreamdownRN, the messages do not appear in chronological order while scrolling, messages show the wrong index/appear out of sequence. For comparison, with react-native-markdown-display directly, the same list scrolls as expected and the indexes remain in the correct chronological order.

• Screen recording using StreamdownRN: recording
• Screen recording using react-native-markdown-display: recording

To reproduce this, hook up the example I’m using to showcase the issue:

chat-history-v2.tsx

This also happens to me. I am using version 0.2, also with flashlist.

Not related but text selection seems to not be possible and tapping links has no reaction. These would be great features to implement. If I can find the time I will try to do it.

[edgarpavlovsky]

thanks guys - taking a look at this today Sent via Superhuman ( ***@***.*** )

…

On Tue, Dec 16, 2025 at 1:09 PM, Joao Terrantez < ***@***.*** > wrote: *joaoterrantez04-ctrl* left a comment (darkresearch/generative-ui#9) ( #9 (comment) ) > > > Hi @edgarpavlovsky ( https://github.com/edgarpavlovsky ) - thanks for the > reply, > > > > I tested again with the latest version. Previously it was skipping/jumping > messages, but now messages get also mixed up and occasionally jump around > when scrolling. I’ve added two screen recordings. In the videos I’m just > trying to scroll up from message 20 to message 1, and you can see the odd > behaviour. > > > > I’ve rendered the index inside each message so you can see that, when > using StreamdownRN, the messages do not appear in chronological order > while scrolling, messages show the wrong index/appear out of sequence. For > comparison, with react-native-markdown-display directly, the same list > scrolls as expected and the indexes remain in the correct chronological > order. > > > > * Screen recording using StreamdownRN: recording ( > https://drive.google.com/file/d/1BIXS7q__gBlDJuyNnU_LZbjUlLbId05t/view?usp=sharing > ) > * Screen recording using react-native-markdown-display: recording ( > https://drive.google.com/file/d/18imd1TKp-6N_od0Q-yGgGDNsoVJhJWeK/view?usp=sharing > ) > > > > > To reproduce this, hook up the example I’m using to showcase the issue: > > > > chat-history-v2.tsx ( > https://github.com/user-attachments/files/23918324/chat-history-v2.tsx ) > > This also happens to me. I am using version 0.2, also with flashlist. Not related but text seletion seems to not be possible and tapping links has no reaction. These would be great features to implement. If I can find the time I will try to do it. — Reply to this email directly, view it on GitHub ( #9 (comment) ) , or unsubscribe ( https://github.com/notifications/unsubscribe-auth/AC32YXXNBKGZQU4YCDJKXM34CBRITAVCNFSM6AAAAACNZYMXXSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMNRSGE4TGMZQG4 ). You are receiving this because you were mentioned. Message ID: <darkresearch/generative-ui/issues/9/3662193307 @ github. com>

[edgarpavlovsky]

@eliasljubec @joaoterrantez04-ctrl - thanks for giving me a heads up on this, i was (finally) able to replicate it!

pushed v0.2.1 which should have relevant fixes -- lmk if this fixes behavior on your side.