intermittent fails/successes when requesting a subset of data using shared dimensions

[Mikejmnez]

The Context

I am attempting to download a subset of a very simple test dataset, with a tree repr as follows:

.SimpleGroup.nc4.h5
├──SimpleGroup
│  ├──Y
│  ├──X
│  ├──Temperature
│  └──Salinity
├──time
├──Z
├──Pressure
└──time_bnds

In this scenario, I want a subset of Salinity, which has dimensions time, Y and X, each a 1D array. NOTE: time has a single value and lies at root, whereas the rest of the dimensions and Salinity lie within /SimpleGroup.

To request the subset I construct the url using constraint dimensions. For example (needs escaping, but this is more readable):

http://test.opendap.org/opendap/dap4/SimpleGroup.nc4.h5.dap?dap4.ce=/time=[0:1:0];/SimpleGroup/Y=[0:1:9];/SimpleGroup/X=[10:1:19];/SimpleGroup/Salinity

the problem

I get intermittent 400 or 200 responses when requesting a dap response using the above url. I tried with pydap ( via requests.Session), firefox/Chrome web api, and curl. When it works (200 response) I get the right thing, but when I get a 400 error ,I get the following response:

<?xml version="1.0" encoding="UTF-8"?>
<dap4:Error xmlns:dap4="http://xml.opendap.org/ns/DAP/4.0#" httpcode="400">
 <dap4:Message>libdap error transmitting DAP4Data: Invalid constraint parameters: At least one of the start, stride or stop
 specified do not match the array variable.</dap4:Message>
  <dap4:Context />
  <dap4:OtherInformation />
</dap4:Error>

Nathan shared the following BES command is:

<?xml version="1.0" encoding="UTF-8"?>
<bes:request xmlns:bes="http://xml.opendap.org/ns/bes/1.0#" reqID="ajp-nio-0.0.0.0-8009-exec-3_32" reqUUID="7611633c-c442-4d16-8ddf-1c60f0d985ff" clientId="/-0" clientCmdCount="16">
  <bes:setContext name="bes_timeout">300</bes:setContext>
  <bes:setContext name="dap_explicit_containers">no</bes:setContext>
  <bes:setContext name="errors">xml</bes:setContext>
  <bes:setContext name="olfsLog">206.192.248.66|&amp;|curl#8#7#1|&amp;|-|&amp;|-|&amp;|1757632470915|&amp;|ajp-nio-0.0.0.0-8009-exec-3_32-7611633c-c442-4d16-8ddf-1c60f0d985ff|&amp;|HTTP-POST|&amp;|/opendap/hyrax/dap4/SimpleGroup.nc4.h5.dap|&amp;|-</bes:setContext>
  <bes:setContext name="xml:base">http://test.opendap.org/opendap/dap4/SimpleGroup.nc4.h5</bes:setContext>
  <bes:setContext name="max_response_size">0</bes:setContext>
  <bes:setContext name="max_variable_size">0</bes:setContext>
  <bes:setContext name="uid">not_logged_in</bes:setContext>
  <bes:setContext name="dap4_checksums">false</bes:setContext>
  <bes:setContainer name="catalogContainer" space="catalog">/dap4/SimpleGroup.nc4.h5</bes:setContainer>
  <bes:define name="d1" space="default">
    <bes:container name="catalogContainer">
      <bes:dap4constraint>/time=[0:1:0];/SimpleGroup/Y=[0:1:9];/SimpleGroup/X=[10:1:19];/SimpleGroup/Salinity</bes:dap4constraint>
    </bes:container>
  </bes:define>
  <bes:get type="dap" definition="d1">
    <bes:contentStartId>22a85fea:1993b0f148a:-7ffd@opendap.org</bes:contentStartId>
    <bes:mimeBoundary>Part_32326138356665613a31393933623066313438613a2d37666665</bes:mimeBoundary>
  </bes:get>
</bes:request>

This may be an edge case. When I consider an example in which all dimensions exist in the same Group in which the data array I am attempting to subset lives, it works every time. But in this scenario where time is at root and the rest of the data is within SimpleGroup, I get this intermittent behavior...