Nextcloud Client crashes after start

Nextcloud version (eg, 20.0.5): 22.2.0
Nextcloud client version: 3.3.6 x64
Operating system and version (eg, Ubuntu 20.04): Windows 10 Pro, ver. 10.0.19043

The issue you are facing:
Im using Nextcloud hosted by the company Hetzner in Germany. I have problems with the Nextcloud client on one of my computers. It crashes right after it has been started. I don’t even have the possibility to open the settings. I already uninstalled the client, rebooted, reinstalled it and rebooted again. When I move the mouse cursor above the icon in the icon tray, Nextcloud client crashes immediately. When I start it manually, I could see the sync icons above the folders and after a few seconds, it crashes again.

I’ve recognized a message in the application event log of windows (sorry, I only have this in German):

Name der fehlerhaften Anwendung: nextcloud.exe, Version: 3.3.6.25940, Zeitstempel: 0x617a888f
Name des fehlerhaften Moduls: nextcloud_csync.dll, Version: 0.0.0.0, Zeitstempel: 0x617a8443
Ausnahmecode: 0xc0000005
Fehleroffset: 0x000000000001a100
ID des fehlerhaften Prozesses: 0x3418
Startzeit der fehlerhaften Anwendung: 0x01d7ef3da25369f5
Pfad der fehlerhaften Anwendung: C:\Program Files\Nextcloud\nextcloud.exe
Pfad des fehlerhaften Moduls: C:\Program Files\Nextcloud\nextcloud_csync.dll
Berichtskennung: f30a4212-97ea-4fed-b292-9c4c353d5971
Vollständiger Name des fehlerhaften Pakets: 
Anwendungs-ID, die relativ zum fehlerhaften Paket ist: 

This is the XML of the error:

- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
  <Provider Name="Application Error" /> 
  <EventID Qualifiers="0">1000</EventID> 
  <Version>0</Version> 
  <Level>2</Level> 
  <Task>100</Task> 
  <Opcode>0</Opcode> 
  <Keywords>0x80000000000000</Keywords> 
  <TimeCreated SystemTime="2021-12-12T09:50:06.3982869Z" /> 
  <EventRecordID>34694</EventRecordID> 
  <Correlation /> 
  <Execution ProcessID="0" ThreadID="0" /> 
  <Channel>Application</Channel> 
  <Computer>DESKTOP-4V2J4CS</Computer> 
  <Security /> 
  </System>
- <EventData>
  <Data>nextcloud.exe</Data> 
  <Data>3.3.6.25940</Data> 
  <Data>617a888f</Data> 
  <Data>nextcloud_csync.dll</Data> 
  <Data>0.0.0.0</Data> 
  <Data>617a8443</Data> 
  <Data>c0000005</Data> 
  <Data>000000000001a100</Data> 
  <Data>3418</Data> 
  <Data>01d7ef3da25369f5</Data> 
  <Data>C:\Program Files\Nextcloud\nextcloud.exe</Data> 
  <Data>C:\Program Files\Nextcloud\nextcloud_csync.dll</Data> 
  <Data>f30a4212-97ea-4fed-b292-9c4c353d5971</Data> 
  <Data /> 
  <Data /> 
  </EventData>
  </Event>

After this a second INFO log appears in the event log:

- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
  <Provider Name="Windows Error Reporting" /> 
  <EventID Qualifiers="0">1001</EventID> 
  <Version>0</Version> 
  <Level>4</Level> 
  <Task>0</Task> 
  <Opcode>0</Opcode> 
  <Keywords>0x80000000000000</Keywords> 
  <TimeCreated SystemTime="2021-12-12T09:50:16.9890165Z" /> 
  <EventRecordID>34695</EventRecordID> 
  <Correlation /> 
  <Execution ProcessID="0" ThreadID="0" /> 
  <Channel>Application</Channel> 
  <Computer>DESKTOP-4V2J4CS</Computer> 
  <Security /> 
  </System>
- <EventData>
  <Data>1773650891753206901</Data> 
  <Data>4</Data> 
  <Data>APPCRASH</Data> 
  <Data>Nicht verfügbar</Data> 
  <Data>0</Data> 
  <Data>nextcloud.exe</Data> 
  <Data>3.3.6.25940</Data> 
  <Data>617a888f</Data> 
  <Data>nextcloud_csync.dll</Data> 
  <Data>0.0.0.0</Data> 
  <Data>617a8443</Data> 
  <Data>c0000005</Data> 
  <Data>000000000001a100</Data> 
  <Data /> 
  <Data /> 
  <Data>\\?\C:\ProgramData\Microsoft\Windows\WER\Temp\WERBBCF.tmp.mdmp \\?\C:\ProgramData\Microsoft\Windows\WER\Temp\WERBD47.tmp.WERInternalMetadata.xml \\?\C:\ProgramData\Microsoft\Windows\WER\Temp\WERBD67.tmp.xml \\?\C:\ProgramData\Microsoft\Windows\WER\Temp\WERBD75.tmp.csv \\?\C:\ProgramData\Microsoft\Windows\WER\Temp\WERBDA5.tmp.txt</Data> 
  <Data>\\?\C:\ProgramData\Microsoft\Windows\WER\ReportArchive\AppCrash_nextcloud.exe_87f14c1997c9ded83a0ed6fdaf6fcb148771c0_14e164ed_46da9255-14da-4d66-be04-76b3e96060b5</Data> 
  <Data /> 
  <Data>0</Data> 
  <Data>f30a4212-97ea-4fed-b292-9c4c353d5971</Data> 
  <Data>268435456</Data> 
  <Data>d021ab21012d25e6089d4616be813475</Data> 
  <Data>0</Data> 
  </EventData>
  </Event>

Since this is a hosted Nextcloud server I don’t have access to the Nextcloud logs.

I hope I gave enough information. Please ask, if you need more. Currently, I cannot sync my files on this computer.

On the bugtracker, there is a hint that it can be related to downgrades with an easy fix:

If not, I’d put my own bug report on the bugtracker. I don’t know if they receive these crash reports automatically, but in the event.log you have links to memory dumps. So perhaps they are asking for them (don’t put them publicly on github, they could perhaps contain sensitive information).