you shouldn't be having any problems because they are all AMD cards.
i'm running acouple mixed rigs without any issues.. i'm assuming your on windows?
have you checked your mobo bios settings?, virtual ram memory are set?
shouldn't be a riser issue, because your cards are detected.
if you have everything setup correctly, possibly a bad card.. I've gotten a few.
check your afterburner if your running it, make sure its not the same settings for ALL cards.
you should provide more details about your setup so maybe someone else can also help you out.
Thanks for your reply.
I am running Windows 10, on a ASUS Prime Z270-P mobo. The mobo settings might be something to check, so I'll take a look later on, however since I can run the 3 other cards fine, and then have a problem while running the Red Dragon with a single other card, I'm thinking the mobo and virtual ram settings are fine ?
I am running Afterburner too, although not at bootup (only manually), so I don't think that has anything to do with it either, but I'll have a look there too.
If it is a bad card, how would I prove that it's bad so that I can return it ?