Right after starting to accept FT8 eQSL decided to upgrade their mode definitions to those of ADIF 3.0.4, so the mode is now "PSK (PSK31)" and not PSK31.
eQSL offers the option to upgrade your outbox, but it seems cqrlog currently is not ready for this change as it does not recognize new PSK (PSK31) contacts at the moment. I saw no announcements from eQSL so I guess they surprised all software developers.
From the eQSL_error.txt file:
QSO NOT FOUND in log
which is in my log as PSK31 at that date/time.