OK formatted the partition again and changed block size back to 1024 (shouldn't matter with PFS3 anyway), then copied back all files. Then ran PFSDoctor and also Diskvalid, no errors found. Still the same. However...
I had set my PPC memory to fastest possible earlier in the ppc-bootmenu (just for speed tests), but I remember having set it back to 60ns. But the setting wasn't saved there, so I can only guess that this faster memory access has MAYBE corrupted some files during backup copying. Damn! Even setting it back to 60ns the freeze happens anyway...
But no worries, I finish my BetterWB installation and make that my main WB 3.1 partition

. I don't mind setting it all up again (WarpUP, Picasso96, Mediator etc.), tinkering is a major part of the Amiga fun! :hammer: