Hi ukus,
I suggest you to reset all the changes you’ve done to Z-Push yourself and leave only those Sebastian and I mentioned. Then remove ActiveSync account from your device and remove device using z-push-admin so that you start with the fresh installation.
However I’m also not sure this will work as BackendKopano had too many changes and probably won’t work with BackendCombined properly. Our suggestions were to work around the immediate issues which occur, but apparently they cause other problems to appear. It’s also not something we will investigate in the near future.
You’d be better of using CardDAV and CalDAV which are known to work well with CombinedBackend for contacts, appointments and tasks. Or you configure two ActiveSync accounts on your mobile - one for IMAP and Kopano for the rest if using Kopano backend only is not an option for you.
Manfred