Is it normal that the rig would crash after some time if I mix hynix and elpida GPUs?

I have 4 Sapphire Nitro+ 570 with elpida memory and 2 Sapphire Nitro+ 570 with hynix memory... if I run them separately then rig is stable, but as soon as I start to mix GPUs with different memory types on one rig... I would see crashes, reboots, etc...

is that normal? Any ideas?