Dear folks!

If BOINC on your computer experiencing a problem during project communicating, try to replace file ca-bundle.crt in programs directory of BOINC (C:\Program Files\BOINC\ca-bundle.crt, for example) by this file: https://srbase.my-firewall.org/sr5/download/ca-bundle.crt and restart whole BOINC processes or reboot computer.

Another threads on forum:
Peer certificate cannot be authenticated with given CA certificates
Wus not uploading
Transient Error
Communication deferred
100% block still crunching

Thank you for participation!

Hallo zusammen,
kurz bevor die Meldung kam, hatte ich diesen Weg schon versucht. Warum auch immer, bei mir funktionierte es nicht. In einem anderen Forum wurde auf https://drive.google.com/uc?id=1-zirSeFwap21lRABRLD6k_nlOHlXRLFe&export=download verwiesen. Damit waren meine Probleme behoben.
Gruß
MSH

There was no need to restart on my end :)
They were finally uploaded (one day late on the deadline)