Files opening as "read only"

Hello! Having an issue that is getting worse by the day, hoping someone has an answer or some suggestions…

I support two small businesses, both in the Architecture field. Over the course of the last few months the users have been reporting that at random times, files they have saved to the EX2 are then opening as read only. Only workaround is to do a Save As and create another file at that point.

They are all on Macs running the latest release of either High Sierra or Mojave, all connecting over SMB. They are using AutoCAD, AutoCAD LT, InDesign, Photoshop, Word, etc. - the read only issue has happened with every kind of file. One of the offices runs Revit in Windows (via Parallels) and I have not heard of the issue happening on those files (not that it isn’t, I just haven’t heard about it but I thought I’d mention it). One has been on the EX2 for nearly two years and never had this occur until sometime the last few months. The other office has been on the EX2 since October and the problem has occured right from the start.

So something is altering the permissions on random files on the server, but I don’t know what or why - as far as I knew the default permissions for the EX2 were read/write all for everything. Any thoughts would be greatly appreciated…

Thank you!