Error upon log in to backend

[Shiraz]

Hi. I've got a new error affecting a working shop. It started today. I have not touched the back end at all.

The issue is that when I try to log in to the backend, I get this error:

There are several errors.

Error found : CData section not finished Reward loyal customers and increase their loyal in must_have_module_list.xml file.
Error found : Premature end of data in tag description line 1 in must_have_module_list.xml file.
Error found : Premature end of data in tag module line 1 in must_have_module_list.xml file.
Error found : Premature end of data in tag modules line 1 in must_have_module_list.xml file.

Does anyone understand what may have happened? Can anyone suggest a way to repair the error?

A secondary issue I have is that the frontend of the shop appears to be working (haven't fully tested, just trying to get back end back up asap). This means that people may potentially be making orders. I can't turn it off because I can't log in to back end and also i have no way of contacting anyone, nor processing any refunds. 

Can anyone suggest a way to fix the error?

Regards,

EDIT: 

Prestashop version is 1.7.5.2. Frontend is still functioning.

Edited November 20, 2020 by Shiraz (see edit history)

[Shiraz]

Solved with advice from this thread (I deleted the file associated with the error).