Next day, the backup was created successfully, but still the same lines in log:

2022-05-07 03:13:06 Exporting old records
2022-05-07 03:13:06 record CClassVc: skipped from export, completely blank header
2022-05-07 03:13:06 record CClassVc: skipped from export, completely blank header
2022-05-07 03:13:06 record CClassVc: skipped from export, completely blank header
2022-05-07 05:37:30 Exporting company 1 SUTURA
2022-05-07 05:37:30 Exporting blocks

/Piotr W.