I purchased 5 and added 3 without issues. These are the 8 scene 2342-222. I have two left and they both fail the same way by adding the B button then failing with a pop up that says "The following device could not be added: 54.bc.39 (2342-222) Mini Remote Keypad, 8 Scene v.39 - Cannot add insteon Device. " and an OK option.
I power shutdown and power cycled the ISSY994i. I power cycled the PLM. I did a factory reset on the two minis. I checked that I only have 87 links so not anywhere near the limit. I moved the mini near several switches to ensure they had good wireless connections. I recharged the mini to make sure and they both have a good charge.