I don't think that the NVidia card, nor having both in one box, is actually the problem. I think that I would have issues with just the RX 5700 as the sole card in the box. AMD drives do that to me, they have over the years on my RX 570 cards, as well as 7950 cards before them. They (sometimes, rarely), simply don't "wake from monitor sleep". I've just come to accept that can happen. Both AMD AM4 and Intel Skylake rigs, so it's not really a system-platform problem. It's their GPUs/drivers.
And, I don't have that many dual-GPU-slot crunching boxes. I have three AM4, and two Skylake rigs, and really only enough room for 3+1 rigs, with one sticking out in my living room, unless I clean off the dining-room table, and put a pair of PCs on there, and run them off of the dedicated A/C circuit. (Which I did last summer, with the Skylake/Kaby Lake rigs mining on my Polaris cards.)
Edit: For clarification, I said "Skylake rigs", because when I first got my Z170 Pro4S mobos, that's what I had in them, Skylake dual-cores, and I OCed them. But technically, I have Kaby Lake non-OC'able G4560 CPUs in them now, so I guess I should have called them "Kaby Lake rigs". I just have a fondness for the original Skylake configuration, I guess, and remember them that way.
Edit: And actually, if you think of "platform" rather than "CPU", I'm not wrong, they were the original Skylake platform (Z170). A Kaby Lake platform would have been Z270.