Yep.

The bike in question I bought second hand. I used an old wheelset and driveline, which was fairly worn. Anyway, I was never happy with the shifting and driveline from day 1.

Bought a new cassette and chain, and it did help to fix the problem, but the derailleur still had troubles finding and staying in gear every so often. Tweaked the hanger a bit and got it set up and aligned the best I could, but still wasn't 100%

Replaced the derailleur hanger and tuned it up from scratch. Bit better, but still not perfect.

Pulled apart the derailleur pulleys to clean them up one day, and that was the final straw. The derailleur did not like that one bit. It was fairly old and worn to begin with, a heavily used 03/04 model Deore XT, but replacing that top bushing with a spare which was slightly too big just threw it all out of whack. Add that in to the aforementioned wear factor, and it just would not stay in gear.

So I got sick of it, forked out the cash and got myself a new SLX.

There's a chance that your Altus may just have been a faulty unit.