On a MS390, the piston got battered by foreign material and stuck the top ring. Saw was very well used and not worth the effort.
The other a MS260 was in for porting and did not make the grade, with hitches in the bottom bearings and such. Another direction was deemed prudent.
It can happen to anything, there's plenty of them out in the bone yard too. Have a used husky inbound with bad compression, hopefully it can be fixed, so it can be ported.
Well...
Have the most beautifully restored Stihl 064 on my bench now that you'll ever see.

Sometimes you're the windshield, sometimes you're the bug.