all cases were with build 8.5 2020-01-07 (build 85330517), some of them upgraded from 8.4,8.2 some (ourselves) from 8.5 2019-11-26. While uprading from build 517 to 524 I have seen many of these in the log:
2020-02-17 12:29:39 (-1) M4JobVc

2020-02-17 12:29:39 (-1) Skipping import of softvar s3uploadi of type with value in register M4JobVc, unknown type.

When at some point after upgrade to build 524 the client became unresponsive, I moved all old TByyyymmdd.TXT to another folder and it became responsive again. That particular client has some very strict cisco firewall. Could the firewall with packet inspection feature be an extra problem?