Zarr file over HTTP fetches several times the same time axis variable

What happened?

When loading a Dataset from Zarr over HTTP the time chunk is fetched 3 times from the remote location.

Example Zarr dataset (on google bucket) :
https://storage.googleapis.com/test_zarr_oie/IEA_PVPS.zarr/ADR/zarr.json

What did you expect to happen?

I expect the following URL to be fetched once only :
https://storage.googleapis.com/test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0

Instead it is fetched 3 times (logs from mitmproxy) :

16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zattrs                                                       404 application/xml  201b 358ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zgroup                                                       404 application/xml  201b 384ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zmetadata                                                    404 application/xml  204b 346ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/zarr.json                                                     200 …plication/json 40.5k 204ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0                                                      200 …n/octet-stream ….04k  26ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0                                                      200 …n/octet-stream ….04k  24ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/station_name/c                                                200 …n/octet-stream   27b  31ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0                                                200 …n/octet-stream ….04k  25ms 

Minimal Complete Verifiable Example

# To spy the request, you may setup a local proxy first : 
# `mitmproxy --mode reverse:https://storage.googleapis.com/ --listen-port 1111`

# Initial URL
# URL="https://storage.googleapis.com/test_zarr_oie/IEA_PVPS.zarr/ADR"

# Proxy URL 
URL="http://localhost:1111/test_zarr_oie/IEA_PVPS.zarr/ADR"

ds = xr.open_dataset(URL, engine="zarr")
print(ds)

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zattrs                                                       404 application/xml  201b 358ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zgroup                                                       404 application/xml  201b 384ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/.zmetadata                                                    404 application/xml  204b 346ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/zarr.json                                                     200 …plication/json 40.5k 204ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0                                                      200 …n/octet-stream ….04k  26ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0                                                      200 …n/octet-stream ….04k  24ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/station_name/c                                                200 …n/octet-stream   27b  31ms 
16:28:07 HTTPS GET    storage.googleapis.com /test_zarr_oie/IEA_PVPS.zarr/ADR/time/c/0

Anything else we need to know?

No response

Environment

Start with the provided xr.open_dataset(URL, engine="zarr") MVCE and inspect the repeated remote request for time/c/0 while loading the example dataset. Confirm that the time chunk is fetched once rather than three times, while preserving successful dataset loading.