Zoom Phone/PBX - Faxes forward to an EMR's fax # being split

I am seeing faxes from Athenahealth mostly but occasionally others, being split into two separate faxes.

E.g. 1st fax pages 1-6 and then a 2nd fax with pages 7-11.

Oddity is that it's also only one specific location/fax line seeing this behavior.

Path is as follows:

Zoom Fax # "X" > Auto Receptionist "X" that forwards to > EMR fax # "A"

This is the one splitting sometimes

Zoom Fax # "Z" > Auto Receptionist "Z" that forwards to > EMR fax # "A"

This one, and many others configured similarly have never seen this issue

This is all within their normal PBX config, nothing related to online fax.

Our EMR vendor is at a loss.

I cannot find any meaningful config differences between other fax lines, and the one with the issue.

(Beyond the obvious like a different fax # and name).

Hoping someone else has seen similar issues? Have not found anything as of yet...