Hello Stefan, for a long time I also had a issue with the Su-25 where if I launched it in QMB I also had a crash at 30%, also tried the classfile as advised but the problem persisted.
Recently some one mentioned they moved their engine mod folder further up the folder and it cured a issue with some types, sorry I for get which, this worked for me for the Su-25, Bede and one other.
My game now has these with only two folders above them, both aircraft:
! SAS_Engine_Mod 2.8.2w_full_20180208
! SAS_Engine_Mod_GuidedMissiles 2.8.2w_full_20180208
I cannot guarantee this will help you, also I do not know if doing this has caused issues to any other mods in my 4.12.2 with SAS ModAct 5.30 game but it gave me a fix to what had been a issue for a long time.
Health issues prevent me doing much in the game these days so my flights usually involve having the AI test anything new I add just to see if there are issues in my game or not. If I was using the game on a regular basis I might have come across other issues but from quick tests I think all the modern jet types are okay.
Hope this helps.
Wishing you all the very best, Pete.