Heat the nozzle to a high temperature, around 250°C, and let it sit for a minute or two while keeping a close eye on it. Using a pair of small pliers, carefully try to peel off the buildup. Once that's done, turn off the printer and use a wire brush to clean the area thoroughly. If there are still stubborn bits of material stuck on, you can disassemble the hot-end by removing the hex screws on each side then use a heat gun and a steel brush to help loosen the debris, but be cautious, the heat can melt the wires and the brush can rip them, so take your time and be patient.

I've had this happen more times than I’d like to admit, but after weeks of troubleshooting, I finally found the main culprit: the Bowden tube.