sudden segfault upon carddav access

[kolab.user at use.startmail.com]

Greeting,

I've been hosting two personal domains on one kolab server. Suddenly CardDAV access to one domain results in 

[core:notice] [pid 466] AH00052: child pid 19145 exit signal Segmentation fault (11)

when accessing from MacOS and iOS clients.

Web console seems fine.

Second domain has no errors and functions properly.

Could anyone suggest debug steps?

Regards,
Josh.