Changes
/* On MiST version */
VRAM mirror is something new since NEXYS2 to NEXYS4 so it seems a good way. => DISP signal not crossed correctly with crtc_W / bvram_W ? crtc scanner offset jumps problem ?
Can look after a old NEXYS4 version, perhaps the first ones doesn't has "internal mirror VRAM", but a clk sequencer in external RAM.
Do check the VRAM write speed also : is still a screen written at 50/60Hz ? do check vertical_counter/horizontal_counter scan related to that.
