Which version of SOGo are you using?

2.2.10

Please provide sogo.log and the raw source of the calendar.
If possible provide a tcpdump of the traffic when the 85010014 occures.

tcpdump -w /tmp/syncerror.pcap -i lo -s 0 tcp and port 20000
Note: pcap contains your password -> use a temporary pwd for the test
On what phone model does the problem occures?

No feedback provided in weeks, closing. Reopen if necessary after testing v2.2.11.