Hi everyone I have nearly give up on my 2005 fiat multipla but going to check if any easy fixes. First off I had clutch cylinder problems fixed this after blood sweat and lots off bleeding! Anyway 3rd gear started popping out (ignored it) then 4th gear popped out (held it into place) 5th popped out. They will all go into gear fine but stay in for very little time. 3rd and 4th stay in longer if held in position. 1st and 2nd work fine. Is this a gearbox problem or linkage. Kind regards

There is a known issue with fourth gear not engaging fully, not sure if it could extend to others, but might be worth a look.
https://www.fiatforum.com/multipla-guides/304653-multipla-4th-gear-repair.html

Other than that, try lubing the Cables, and check your Engine/Gearbox Mounts for play.