.... All looks good. Few freezes and eventually system starts. Card gets recongnized after few mins, done DDU, reinstalled GPU drivers. Problem is then I'm mining even desktop lags a lot and mining performance is like 10 times slower on all cards.
This is weird, if it
freezes sometimes, there's really a problem.
But seeing that the your rig starts, this might be a power issue, not your PSU but maybe from the
riser, it wasn't
powered.
The MoBo's PCI-e slots are powered which is used by the GPU, those 8-pins power connectors are the
supplementary power.
You can't use the cards properly with incomplete power source, it could be the riser, it doesn't supply the power from the PCI-e slot.
Could Windows reinstall help? Maybe it has to be installed while that pci-e card connected? I'm out of ideas.
Not at all, you can plug anything without needing to reinstall Windows..
It doesn't look like a software issue to me.