Same problems here, Ubuntu 18.04, also freeze after the login screen, not able to rectify!. I tried/checked everything mentioned above, the problem remains the same. Please see if there is something else in the bug report.
nvidia-bug-report.log (835.2 KB)
See the original question please:
https://forums.developer.nvidia.com/t/after-doing-prime-select-nvidia-blank-freeze-screen-after-login/121050