Culpit seems to be the Survival-Mode-Improved-SKSE mod according to the logs, disabling it solves the issue. My Septimus installation is in the C: drive, but mod download folder is in the D: drive. Don't know why the log mention the D: drive at all there.
After doing a clean installation of Septimus 4.2.0, I can't enable survival mode without crashing to desktop.
Here are the steps I did, not sure if all are needed to reproduce the issue :
People have reported the issue on multiple races or starts. Log of the crash : https://pastebin.com/raw/i8im1rhL
Culpit seems to be the Survival-Mode-Improved-SKSE mod according to the logs, disabling it solves the issue. My Septimus installation is in the C: drive, but mod download folder is in the D: drive. Don't know why the log mention the D: drive at all there.