update:
first installed POD HD Edit - then connected to line6 HD Pro. After that Monkey accepted all updates (incl. drivers) Don't know why, but everything is fine now (MacMini with 64bit)
this is a problem since Mac started with 64 bit - there are problems all over with line 6 software (I upgraded on high Sierra/Mac mini late 2011) - its on you line 6 and for all your costumers to fix the problem.