I also think MAYBE it has something to do with the size of the media you are playing it from? Not sure? I have a 128gb SanDisk Micro SD card with all my retail games on. But for the Atomiswave games I am using a Kingston 4GB SDHC Class 4 MicroSD card from a first gen GDEMU clone, all 3 games ran amazing for me, literally zero performance issues. I am guessing smaller cards may have better read times? I do know over at Dreamcast-Talk people were having issues with large SSD's even on the MODE, and larger SD cards on GDEMU as well as one guy not being able to play this particular game at all on his USB-GDROM who I spoke to over at reddit. So something has to be going on and there must be some common thread as to why this is affecting some users while not others like myself?
I wondered something about this game when I was researching about it a week ago. It said the game supports force feedback on the steering wheel. This made me wonder if that code could be adapted to work on the Dreamcast Rumble Pack to have a more feature complete port?
It also has system link over the Atomiswave communication cartridge connected to a router which I only discovered after downloading and reading through the official game manual. So would be interesting to do tests between 2 consoles with BBA over LAN.