I added some info to the GitHub issue tracker. Also tried reverting the cave games to the files you provided (thanks!) but the issues remain unfortunately.
Back to the problem with APB not starting - looking at the github issue tracker for the Raizing cores I found this[*] closed issue which isn't really all that encouraging. Seems to be a common problem. psomashekar commented "Unfortunately not much we can do about this as it is an sdram issue. Sorry about that.".
Buying more SDRAM and hoping to get one that is compatible seems to be what they suggest. Aargh!
[*] https://github.com/MiSTer-devel/Arcade-Raizing_MiSTer/issues/17
Back to the problem with APB not starting - looking at the github issue tracker for the Raizing cores I found this[*] closed issue which isn't really all that encouraging. Seems to be a common problem. psomashekar commented "Unfortunately not much we can do about this as it is an sdram issue. Sorry about that.".
Buying more SDRAM and hoping to get one that is compatible seems to be what they suggest. Aargh!

[*] https://github.com/MiSTer-devel/Arcade-Raizing_MiSTer/issues/17