Running version:

ii sogo:amd64 3.1.5.20160823-1 amd64 a modern and scalable groupware
ii sogo-activesync 3.1.5.20160823-1 amd64 a modern and scalable groupware - ActiveSync module

Aug 23 15:38:07 sogod [13815]: <0x0x555f50f6e480[SOGoActiveSyncDispatcher]> Change detected during Sync, we push the content.
Aug 23 15:38:07 sogod [13815]: [ERROR] <0x0x555f51bfbc40[NSDataMalloc]> xml2wbxmlFromContent: failed: Parsing of XML Document Failed

debug'd the EAS and with xmllint --format found:

542d_1d6c9f9a_0.data:1: parser error : EntityRef: expecting ';'
Name><JobTitle xmlns="Contacts:"></JobTitle><Email1Address xmlns="Contacts:">m&k

The particular user (my wife..!) has a contact with an ampersand in the middle. The email address and contact is in the format of m&k@subdomain.domain.tld

I've temporarily removed the ampersand (&) from the contact and it appears to be working ok for now. Suggest we see whether we can escape the ampersand within the xml?

We should be escaping with the following:

Ampersand—&—&
greater-than—>—>
less-than—<—<
apostrophe—'—'
quote—"—"