Had the same issue with a car. Car drove faultless for 2 weeks, but only on short journeys, then it was on a long run, stppied and failed on restart. P601. EEPROM reflashed and car was ok but checksum error still there if long run repeated. It seems that with tunerpro (assuming your using it) if you try and change too many maps at once then checksum this error occurs. Modify a single map, save and checksum and it'll be fine. Modify 5 or 6 in one go then save and checksum and it'll cause this issue.

If you're starting with an ori and then copying modified maps overs, do it singular, save and checksum one by one. Problem should get resolved

This case is very simple. Said user is copy pasting stuff without understanding what he is doing, and he is copy pasting a change in code area.
Which obviously makes the ECU crap itself, regardless of checksums.

Furthermore he is openly admitting that he is stealing this data from a tune he read off some other car and trying to copy it...

Simply as stated the file you have is probably corrupt, there is a checksum which only gets activated after a period of time, like I said you can drive the car for months then do say a long journey or something similar and it'll corrupt. Why this happens I don't know!

Only way to fix, is to flash the EEPROM with a virgin flash or the original, then reload a new flash file made from scratch and checksum'd through each map change. If you continue to use the same flash on say another Ecu the problem persists.

The current file I have had this issue it passes all checksums and the me7checker, I can recreate the problem by taking the car for a 30minute drive, it then fails. However, if I copy each changed map 1 by 1 check summing as I go its fine! Do them as a multiple batch it fails go figure.

I suggest you ditch the file and start again.