Error 500: Internal Server Error Error: Cannot open script file /var/www/html/admin/login.lp

This is default.

Okay, but this may not be the final solution ... when the issue happens again next time, please try to upload those lines somewhere securely for us, e.g., in a zipped text file either uploaded here or via a direct message (there should be no privacy-related content in the data)

Thank you for the file via DM. The bug is indeed a slow exhaustion of available file points in the way FTL interacts with the kernel using netlink. Fortunately, the fix is very simple:

Wahoo!! Thanks. I will stop poring over my journalctl and trying to decipher everything..