Hello bdbrown and mrtom414, and thank you kindly for your reply.
I’ve updated Hueman to the last version today, this does not solve the problem.
I’m using Code Snippets to add code to functions.php, but I have already tried to disable all plugins, including Code Snippets. I also tried reinstalling WordPress and Hueman and deleted my child theme. Nothing seems to work.
Of course, I always make sure to clear all caches and WordPress transients.
I’m afraid that all that is left for me to try is to recover one of my backups and just try again I guess. I just wonder what it could be, chances are that the problem eventually returns.