Windows 10 SMB cannot connect to shares on my Synology NAS anymore

For years I have a Synology NAS running in my network for various uses and it is accessed by multiple devices. Recently, a package on the NAS was causing a slow performance, with the interface loading slowly and streaming files not working. Also, from my Windows 10 PC, that used these shares for years, the Explorer was taking a long time to load and eventually gave the message "Windows cannot access \192.168.1.3\Photo_archive". The problem with the package on the NAS was eventually solved and the NAS has been working properly for about five weeks now. However, the network share on the NAS is still not accessible from the Windows 10 PC, but can be accessed from other Windows 10 and 11 machines on the network.
The error I get (after waiting for a long time) is:
System error 67 has occurred.
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The network name cannot be found.
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From the same machine I can ping the NAS, the SMB ports are open, I can browse the UI via a browser, connect to the NAS via FTP. Only when I try to use Windows explorer (or play some music from the NAS via software that had files in the history) it eventually 'times out'. Also I cannot access SMB shares on other machines than the NAS. I can use SMB on this machine when I install a third party client (muCommander in this case). Therefore I do not think it has anything to do with my network setup, but really with that specific Windows 10 machine.
Also from other PCs, media players or phones in the network, I can use the SMB shares on the NAS just fine (with the same user).
I suspect that the Windows 10 machine has mixed something up and the problem is with the PC/ Windows' SMB service.

When the problem started I did not do any updates or setting changes on the Windows 10 machine, the router or NAS.

Does anyone have any idea how I can reset that, without reinstalling the complete machine?

The hardware/software:
Synology DiskStation DS420+ (setup to support SMB2, SMB2 and large MTU, SMB3)
Windows 10 Pro build 19045
Intel(R) Wi-Fi 6 AX200 160Mhz network adapter
Unifi USG with Unifi components
I have tried various troubleshooting steps such as:
restarting the NAS, router, PC
clearing SMB cache on NAS
accessing via hostname
network resets on the Windows 10 machine
checking the SMB log on the NAS
Reinstalling the network adapter
Trying a different network connection on the PC
Tried via Wi-Fi
Turned off IPv6
Changed the hostname of both the NAS and the PC
Changed the IP address of both the NAS and the PC
Repair the PC via DISM
Remove temporary files
Installed SMB v1 (not enabled on NAS, but tried anyway)
Disabled all firewalls
But none of the above have worked.
Thanks a lot in advance! Let me know if any information is missing.