We've just migrated around 100 accounts from Kerio to Grommunio and we also see lots of sync issues over the EAS interface. Outlook of course, but e.g. also on Mac if we connect the accounts via Exchange instead of IMAP.
So I'm afraid it's really related to the EAS part of Grommunio.
The latest update from this week doesn't help either.
Also it doesn't only affect the calender, but also mails older than 11-12 months (can't be defined exactly, sometimes two mails from the same day a few months ago behave differently, one loads, the next only shows headers.
Are there any known/supposed workarounds for this?
It's actually quite disappointing how unstable this seems once it's running with more users (as we've had id running with 10 users for a few weeks with no issues).