cardDAV sync stuck (again)

hullo group, seems a while ago my cardDAV sync got stuck, new contacts for my desktop computer will not show up on the phone, new contacts from phone will not show up in the cloud. (I had unlikely issues with Google sync this is why I migrated to cardDAV). Is there a simple trick to make cardDAV work again? Sony XA2, #Sailfish OS 3.4 is what I use.

Not an expert at all, but maybe deleting those sync files will help:

https://jolla.zendesk.com/hc/en-us/articles/202530688-How-to-heal-Google-calendar-or-contact-sync

(Not Google, CardDAV in this case.)

does not seem to do the trick, must try again.