one-way sync only for large contact records, from server to phone, but not to server

I have several months worth of contact edits (mainly in the notes field) which don't seem to be syncing to the server. I've tested the other direction: from server to phone and that works. I can create small test contacts on either end and they sync, but existing large contacts don't update from phone to server. I'll need to export my phone contacts for safekeeping then fix the issue then repopulate the server db. Any ideas what is happening? I am the only user on this server, and I'm only using contacts/calendar at this point, no email.

moto g5 plus
android v7
using an exchange connection to zextras/zimbra (not google)

zimbra v8.7.0_ga1659.foss
zextras 2.10.0 (zxmobile license)