SATA cables and splitter are first place to look in your description. If the GPU runs for 72 hours in the motherboard slot directly, its power, riser, cables.
From Discord FAQs:
Common Errors/FAQ
GPU temperature 511 is unreal
511 is a GPU error, more precisely, it’s a power disconnection malfunction, in which the software attempts to query the GPU and gets either nothing or invalid data returned.
This is generally caused by a bad riser/cable(s).
Ensure to check your cables and avoid using SATA to power up risers.