I know that ChaseHQ and Arkanoid looks great, so double RAM buffer (from &8000 to &BFFF) is actived, but normaly it shall unlock XOR and P47, so this second RAM part is perhaps badly plugged (A14 inversed ? WR on one and RD on another, double WR on one ?, bad memory size ?) => VRAM is plugged correctly.
About Xor, do test a RAM Dump.
The SDRAM patched in order to write RAM under ROM is not implemented in VRAM mirror. Behaviour to check. => light version, with fix RAM 0 1 2 3 and quicker address solving does exactly the same, so the bug isn't by here.