Thank you David!
If you could download the model and check it yourself - there is something else than OpenGL messing up. If I export the model geometry to a new file, then everything is ok.
If I export the model to sketchup from old file, the file is unusable - check the image (this is taken from another file, where I had the similar problem).
If i export the model to sketchup from that new file, everything is fine.
So I thought, that I would use the new file, but copying the info from old to a new file takes quite a lot of time. Still - I did it. After finishing with all the importing (schedules, worksheets, details, sections, elevations, layoutbook) the trouble was back - the file was again messed.
I don't use SketchUp, so cannot comment about its issues. But since exporting to SkecthUp should just be the 3D Model (no schedules, details, etc), a quicker solution is to Merge the old file into a new file, which will transfer the 3D Model, then use this file for the export to SketchUp. Keep using the old file in ArchiCAD, then Merge again when needing to export again.
Thank you again;
still - the main problem is not the trouble with export, but the way archicad acts in 3D (the textures) + 2d artifacts. If you check the pic attached - I marked the things, that shouldn't be there.
If you can open the file, see for yourself. May be my PC has gone mad.
There was also a problem with the file in archicad, that it didn't display window markers (checked model view options + window prefs.) copy to a new file worked well.
the merging - can one also merge sections, details, layoutbook etc. ?