Yes, i know, thanks for the tips and i hope it helps someone.
It's one of those pitfalls for the less experienced (i started in TP times)
When in doubt i always do a cleanup and build, especially when switching target platform(s) and or debug to release modes (including fcl / lcl) just to be sure.
In my projects i also use cpu + platform dependent unit output directory's in a dedicated folder i can clear beforehand (its actually on a tmpfs / ramdrive on my system).
Also keeping paths short without spaces and special chars does wonders...
Again thanks all for taking a look and coming forward with suggestions and possible solutions!