A321- auto pilot

Hi all hope you had a merry Christmas
Not sure where this topic belongs so sorry if it’s in the wrong one
I’ve been having trouble with the a321 auto pilot recently.
Last night I was flying at FL-300 at Mach .84 with 68% load, about 15 minutes after I hit cruise altitude it started jerking up and down, which I know had been a problem in the past but haven’t flown this plane for serveral months
So I dropped it back to Mach .82 and it settled down for about 10 minutes and started doing the same thing, so I dropped it back to Mach .80 and descended to FL.280
It was fine for 30 minutes until I fell asleep and woke up to saying it crashed 6 hours later
The whole flight was over ocean and tanks full when I departed, 7.5 hour flight and had 11 hours flight time so unsure as to what could have caused it to crash
Any info would be appreciated
Thanks

Mach .84 is way too fast. Try .78-.79, this will help. On longer routes take steep climbing into account. Hope it helps. :)

Heya, this is a known issue with the A321, please refer to this post by Deercrusher:

Have a good day!

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A321 Autopilot Bug Multiple reports on this

This is a known glitch with the A320 family. The best thing you could do to make the jerking stop during cruise is unselect the altitude hold button and just keep the vertical speed at 0 so you don’t experience the jerking/unusual movements.

Thanks for the replies

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