Sounds (to me) like a power supply issue… What brand supplies are you using? Meanwell? Opto?
I’m thinking that it might be a noise issue… Do you have an oscilloscope to check for noise on the rail?
Might be worth putting an error code trap in. I understand what you are saying, there is no error when you download, it comes some time latter, might be worth trapping that code and putting it in the Que so you can see it latter; Error code decoder