Shannon W on "Loop error_log file won't stop growing."

I would try updating wordpress again.

In dashboard -> updates, there is an option to "re-download" and install Wordpress. Hopefully, it can reinstall that file with the most current.

To be absolutely sure, I'd download wordpress locally, find the file (plugins.php) and manually upload and overwrite the file.

Then, I'd install gotmls plugin and run a scan to see if you have been hacked.

Then perhaps turn on debug mode (https://premium.wpmudev.org/blog/debugging-wordpress-how-to-use-wp_debug/) and see if you've generate more info on the issue.