Created attachment 110255 [details]
Error popup is attached. Output to terminal is
QThreadStorage: Thread 0x7fb8c0c5a100 exited after QThreadStorage 12 destroyed
digikam is set to use a mysql server for the database
downgrading to 5.7.0 results in a working digikam with the database intact.
Please replace the dbconfig.xml as described in this bug 388977 report.
The replacement dbconfig.xml solves the problem, thanks.
In case this matters I am using digikam on fedora 27, which was updated by dnf today. The rpm is digikam-5.8.0-2.fc27.x86_64, built on 18th January.
*** This bug has been marked as a duplicate of bug 388977 ***
Fixed with #388977 and not reproducible with 6.2.0