I've put the latest JagGD firmware live. This improves game support for CD games such as VidGrid and World Tour Racing (which previously did not work) and adds memory track support. And importantly for developers, it fixes instability errors with PC uploads.
Stability is still sketchy, but from all the digging I've done, I believe the issue is actually the Jaguar. So I'm not sure what more I can do, however I'll still be looking into it further.
As usual, hit OPTION when prompted when booting your cart and follow the URL / QR to update.