Well, the good news is that I located what triggers the problem, so I don't need to continue debugging asm 68k
The problem is somewhere in p96 driver. The same sequence works on amiga chipset driver and on linux hosted driver, but fails on p96. The system actually continues working, you just can't see anything that is displayed. I'll look into the driver issue.
In fact the Video Card on AROS 68k has never worked well, many software have jerky graphics, see AmigaAMP, Dopus4 and many others.
I would like to point out that on AROS 68k the Picasso96 software is not installed! on WinUAE the only working Video Card is UAE-GFX (UAE Zorro III) which is automatically recognized without the need for software
On FS-UAE I don't know which Video Card is recognized, on my Amilator that uses FS-UAE AROS 68k it doesn't work and I think it depends on the unsupported Video Card.