Have you tried using Wordfence's high sensitivity scan?
You could easily repair or delete infected files on your WP.
The only tricky part is if the malware source code/file is still in the website file somewhere, but Wordfence can’t access it.
Malware will keep coming back or regenerate itself even after removal.
But hey, it's worth a shot... Simply run the scan and repair/delete the infected files.
That may resolve your issue.