BT keyboards - missing keystrokes - New Mac Mini

I just purchase 4 mac mini's for my Business and my battery powered BT key boards and one USB charging BT unit will not work properly with the new Mac Mini's...it will miss numerous letters...I also bought a new USB charging keyboard that of course works perfectly, issue seems to be universal across all machines.. Did the BT spec change that isn't compatible with older BT keyboards? Really not happy to buy 3 more new keyboards...all software is updated.....Thoughts?