Sharing docs, Editing errors, Docs erased

I am new to using Nextcloud. I am currently running Nextcloud via one of the providers, Cloudamo. My desktop is running Linux Mint mate the latest version 20.1.
The individual that I am sharing the files with is from my contacts and a nonregistered user running Windows 10

We are both able to create documents edit them and sync them to my desktop.
When the folder and its files are shared with an individual in my contacts but not a registered user they can see the files and make edits on the documents create documents and upload new documents within that shared folder. Sometimes when the files have been edited and then viewed again there is an error that pops up and the documents are essentially erased. Sometimes the documents won’t save previous edits even though the file is set to autosave. See image.


This has happened several times randomly and I can’t figure out how or why this is happening.
I have seen full several days worth of work simply vanish with no recourse to the previous save file.

Any assistance in figuring out what is causing this to occur and how to fix it would be greatly appreciated.