Calendar events missing on mobile web client

[Labsy]

Hi,

our Zimbra 8.8.12 begun acting weird all of the sudden. We did not change anything, except we rebooted it once (shutdown/power up) due to moving to another ESXi 6.5 host.

Problem?
Only on MOBILE WEB CLIENT Calendar events are not shown entirely, some events are missing. Users have 4 shared calendars in use, but latley and only on mobile clients, SOME of calendars only show SOME of events. Even more weird is, that among different users, different calendar events are missing.
While on computer, normal web client, all looks fine.

What I tried already?
- Tried with different mobile browser, same story
- tried on numerous different mobile phones, same story...random events missing
- tried with different mobile templates (tiny, standard, ios, mobile...), but same problem
- tried switching web usre interface to another language, but at no avail
- reindexed user mailbox, no joy
- removed and re-added shared calendar share....this helped for few hours, then after 1 day events are missing again
- upgraded ZCS from 8.8.12 to 8.8.15p1, but still no joy

Any idea?
Known problem?

[gabrieles]

Got the same problem but on Activesync side. Only upgrading to 8.8.15 solved the problem.

[Labsy]

Unfortunatelly, not even the upgrade or reindexing (shared) calendar account did not help.
Any other idea? Anybody?