I have the same problem, printer error 031002.
For Epson XP-15000. Windows 10. My printer is fresh, new from the box, with no modifications when this occurs.
I think I have found the pattern as to when 031002 occurs.
The error appears every time any Maintenance function is activated from the printer's little screen navigation. (I don't know about from Windows 10 Epson window navigation, I have not tried.)
Even changing the ink cartridges will cause 031002. It appears with original Epson cartridges AND with FullColor CISS cartridges. Official Epson cartridges or 3rd party cartridges all create this error.
I can delete the error by a long process of reinstalling the original Epson Firmware again. Then restarting the printer. Then reinstalling the Chipless EPFWUPD.exe again, following the instructions precisely. Then whichever ink cartridges are currently in the printer must stay in the printer. Any attempt to touch the Maintenance functions on the little screen to change the cartridges, or check ink levels, or check alignment, or check the printheads, or clean the printheads, will bring 031002 again. Then the painful process of starting over by reinstalling the original Epson Firmware must begin again.
I did not see an option to buy a forever Activation Code, which I had intended to buy. Now that I know I need it to keep this current version of the Chipless EPFWUPD.exe functioning, is it possible to purchase "forever" for the extra $5 or $3 or whatever the difference is? I would also happily repurchase everything again if necessary if there is an update/fix/patch for this Error Code 031002.