Open to that possibility. But in hindsight I did have the exact same issue with my previous IIe enhanced as well.

In fact I do on some occasions get an IOU error "IOU FLAG ES: 1" but most likely this is normal behaviour after running programs and trying to run the self-test.

If you have been running a program, some soft switches might be on when
you run the self-test. If this happens, the self-test will display a message
such as

IOU FLAG ES: 1

Turn the power off for several seconds, then turn it back on and run the
self-test again. If it still fails, there is really something wrong; to get it
corrected, contact your authorized Apple dealer for service.

I found 4 bad DRAMs this afternoon and replaced them with the pulls I had lying around. It's nice to have a second working board ready to go if I need it.