In my experience the hole that the thermistor goes into isn’t in the path of the filament. So probably what’s happening is either the nozzle or the tube that screws into the other side of the heater block is loose, allowing melted plastic to escape through a place other than the tip of the nozzle.

After you’ve cleaned it out, what I like to do before running filament through again is to turn the hot end on, let it come up to temp, then tighten the nozzle a bit more. The joint expands when heated so even if you’ve got it right at room temp it can still need tightening at the working temperature.

That’s filament leaking out, if it’s coming through your thermistor that’s a sign that your thermistor might be loose or something? You might need to disassemble, clean, and reassemble your whole hot end.

I would stop using it for now and replace the extruder if I were you.

I didn’t know but it doesn’t look good! Is it the same color as the filament you have in?