If it is a ringed version some have lower compression on start-up to counter starting issues like seen on some ABC larger engine which can be rough on your starter shafts. But it sounds like you need to check-re-torque all engine bolts especially head bolts and go from there. If it really seems to have a loss of compression you might need to tear-down and check the ring in F series and if ringed version of newer OS, or if ABC which most are on newer engines look at the piston & sleeve to look for damage or wear and check to see if you need a piston or liner or ring..according to if it's ringed or ABC type engine..

This is after you exhaust all other issues addressed here first..