Are you saving to a network drive or to something that’s being synced with a service like DropBox, OneDrive, GDrive, etc? Something is corrupting your file and often those are the culprits.
When when you say “tried a different laptop” do you mean tried opening these files or tried saving files and having those newly saved files come up with this error upon re-opening them?
Because if you get that error opening the file on one machine it will absolutely happen on another - the problem is not with LightBurn, it’s with the file itself - likely it’s just missing data at the end of the file.
Could you upload one of the files in question here for us to look at?