The splurging of plastic from the printer keeps happening. I'm pretty sure my theory about excess material in the nozzle was bullshit. I'm now thinking that the problem could be temperature-related.
There's a lot of plastic coming out in a short time, and its consistency is different from any extruded PLA I've ever seen. I don't think this could be happening at normal temperatures, so maybe there's a problem with the thermistor, or a temperature gradient between thermistor and nozzle caused by environmental factors.
I'll try to find a fitting cardboard box to improvise an enclosure to see if that helps. If not, I'll have to look into the thermistor.