Havoc
I had the same problem on our new 135T2 (35hrsTT when it started to happen) a few month back
EC engineers tried replacing AHR1 under warranty but the problem remained even with new AHR1's; then a bright avionic engineer said it was the AP computer causing the problem. Senior EC staff did not believe him initially but when they changed the AP unit with a new one, it worked lol and has since with no further issue
Hope this can help you out
WLM