Open changesets don't show up in the upload dialog

[gaben]

What steps will reproduce the problem?

1. Make some changes, upload and don't close the changeset
2. Make changes again
3. Try to upload to the same, still open changeset
4. Click on the changeset refresh button

What is the expected result?

The changeset created in 1. step shows up in the upload dialog changeset list, upload to the same changeset possible. The changeset refresh button works.

What happens instead?

The changeset doesn't show up, as if it would be closed. Clicking on the changeset refresh button results in a dialog, saying "No open changesets" or similar.

Please provide any additional information below. Attach a screenshot if possible.

After JOSM restart, the (still open) changesets always show up.
It's not always reproducible.
Also, it's a long-standing issue.
#19780 may be related.
In Postman, the OSM API returns the expected result in reasonable time.

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-11-12 11:23:59 +0100 (Fri, 12 Nov 2021)
Build-Date:2021-11-13 02:31:03
Revision:18323
Relative:URL: ^/trunk

Identification: JOSM/1.5 (18323 hu) Windows 10 64-Bit
OS Build number: Windows 10 Pro for Workstations 2009 (19043)
Memory Usage: 2390 MB / 7266 MB (1279 MB allocated, but free)
Java version: 1.8.0_311-b11, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1920×1200 (scaling 1.00×1.00)
Maximum Screen Size: 1920×1200
Best cursor sizes: 16×16→32×32, 32×32→32×32
System property file.encoding: Cp1250
System property sun.jnu.encoding: Cp1250
Locale info: hu_HU
Numbers with default locale: 1234567890 -> 1234567890
VM arguments: [-Djava.security.manager, -Djnlp.application.href=https://josm.openstreetmap.de/download/josm-latest.jnlp, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlp.tk=awt, -Djnlpx.jvm=<java.home>\bin\javaw.exe, -Djnlpx.splashport=54425, -Djnlpx.home=<java.home>\bin, -Djnlpx.remove=false, -Djnlpx.offline=false, -Djnlpx.relaunch=true, -Djnlpx.session.data=%UserProfile%\AppData\Local\Temp\session524324530548763547, -Djnlpx.heapsize=NULL,NULL, -Djava.security.policy=file:<java.home>\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.origFilenameArg=%UserProfile%\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\31\583aa85f-4236f0ee]
Dataset consistency test: No problems found

[marcello@…]

The changeset reload button depends on network availability. See if the API server is good. Also, changesets timeout on the server all by themselves.

[gaben]

Before writing the ticket I checked the OSM API and it returns the expected result, so it's a JOSM thing.

Updated the ticket according to this.