Where did you get the 5101 chips from? If you flip the chips over do the markings in the plastic look the same? There are lots of fakes and remarked 5101 chips out there. Some are 5101 chips but slower speed chips that may only work reliably in an MPU-100 or Bally board. I’ve also heard that some are 2101 chips or just dead.

Any that are laser etched are going to be remarked chips or fakes. May or may not work. I seem to recall getting a batch that did have printed white markings but they were off a bit and ended up being earlier remarked chips. Often that will wear off much easier than the original printing.

From the pictures posted they look like they should be real chips but you never know. There are so many fakes floating around that every chip has to be tested. Can no longer assume a supposedly new chips is good. If they were ordered off ebay from China or from Aliexpress then the likelyhood of fakes goes up a bit.

I just ran into a batch of 20 fake 6802 chips from ebay (all dead) that I had to open a case on.

The memory chips the original poster has may be ok but I had to raise the issue since it is coming up more often and if those were fakes then possibly chasing a board issue that is actually ok.

They are probably ok then. But had to mention it was a possibility.