For us, Multiline text fields with Append Changes to Existing text works fine in our O365 forms. However, it completely crashes out when an NAC workflow writes to ANY list field for the current SP Online list item.

For example: if our multiline text field is called “AllOurText” and we have a datetime list field called “ReviewerDate”, if the NAC workflow updates “ReviewerDate” without touching “AllOurText”, it still somehow corrupts “AllOurText” so it loses the ability to display all the appended changes. If the NAC workflow doesn’t write to any list field for the SP Online list item, the append changes still functions properly.

Hi @FireMyst,

I have been doing a lot of testing, and it appears that your diagnosis is not correct.

Starting with Nintex for O365 Forms, these forms do not handle SharePoint's Append feature and treat a Multiple lines of text (MLT) column as a normal column. If you use SharePoint functionality, you will see that every update to this column will show the user who updated the column, the date and time, and the update.
Using a Nintex form does not do this.

Nintex Automation Cloud clearing MLT column when updating the item.
Yes, this does happen.  But if you edit the item in Grid view, this also happens, so it's not particular to Nintex Automation Cloud.

Conclusion:
If you don’t use a Nintex form on the list and update the item with a Nintex Automation Cloud workflow, 
The append feature will work as designed by SharePoint and the column will not clear when other columns are updated. 

In other words, the issue here is with Nintex Forms for O365, which was never designed to work with the Append feature of an MLT column.