Is this the first time you've used DisplayPort on that GPU and motherboard? It could also be the motherboard doesn't understand how to send output to DisplayPort during POST.
That's a fair assumption. I guess I would just do some searching around to see if anyone has had a similar issue with either that board or GPU. I think it's unlikely you'll be able to resolve it though. You already have the latest BIOS so if there aren't any settings in there to improve compatibility you might just have to switch to HDMI when you need to access the BIOS.
I was thinking you might switch temporarily for BIOS access, then switch back the rest of the time. You could even leave both cables connected and just switch inputs on the monitor so you don't have to climb around under a desk.
I'm not sure what version of HDMI that card has but you might not be able to get 1440p@175hz. However you likely aren't getting that many frames in newer games anyway. So it might not feel all that different.
You may need to update your GPU's DisplayPort firmware. See here: