I have seen behavior like this in the past. Essentially, upon startup, pinetmgr is failing to create the IPv4 listener, so no connections can be made.
There is probably a delay for the listener to open, so pinetmgr is unable to create the SPN. I would recommend adding a startup delay to the pinetmgr service.
Let me know if that works!
the work item WI102768 you mentioned was the correct hint. The issue actually occurred because of a too early start of the pinetmgr-service. First I wondered why this happens in our system, because the startup of our PI-Server is done by a scheduled Task which calls pisrvstart.bat after waiting 2 minutes and resynchronizing time with the domain. But 2 PI-related services, which have a dependency to the pinetmgr-service, had not been set to starttype "manual", but were still configured as starttype "automatic". Therefore the pinetmgr-service had been started before the scheduled Task calls pisrvstart.bat. After setting also these 2 services to starttype "manual" the pinetmgr-service succeeds in registering the SPN.
Thank you for your help and kind regards