Current Moodle version Moodle 3.10 (Build: 20201109). Adaptable theme version: 3.10.1.1
Good morning,
I just uploaded 4 new users by dropping a txt file on the upload field. This is something I often do. It then highlights all of the entries saying there was some problem but that it has corrected it and now all is good. But today, I got this ugly thing as well. 
Yet, when I checked, the four new users were uploaded into the system as if no coding error had been detected.
James