Glad to be of assistance, hopefully that fix will sort out the flickering issue. I doubt it has anything to do with the other stuff though
About the games locking up, I'd make sure the game files are ok in winUAE, try and create a config as close as possible to the the real A600. Other titles are working ok?
See if they work from IDE on the real amiga too. I admit I didn't try very hard but I couldn't get WHDload to work when the games files were on a PCMCIA memory card. I gather plenty of people have this working but these cards can always be picky about how well they will work with different hardware. I've had CF that won't work on IDE when the ACA630 is on, others that work everywhere except PCMCIA etc . . .
A pic of your card might help. Which corner is sticking up? There is one component on the motherboard which is in the way of the socket, normally the clip on boards from Jens or Kipper have a notch cut out to sit over it, maybe you're one needs a little filing to sit flush.
Probably worth reseating it anyway, these cards are freakin great but basically a hack at the same time, always likely to suffer from contact problems. If you can't get a memcheck to run forever but other stuff is reliable enough for regular use, I'd just go with it. I wouldn't fancy using any clip on card for live music like you do though.
You may find it gets better with time, my ACA hasn't been reseated in over a year now. My theory is that the socket and CPU flex together over many temperature cycles and eventually stabilise, maybe forming some kind of cold weld on the pins. Once in a while though it still bombs out to a yellow screen and won't recover without a power cycle.