Maybe time to replace the nozzle and/or heat break? When was the last time you replaced either of them? The heat barrier loses lubricant internally over time and can cause greater resistance during extrusion. Some people took a (no lint) cloth and some mineral oil and lubricated the filament which works it’s way into the heat break to re-lubricate it. I tried it and it did no harm, seemed to make extrusion better (but I had a whole other issue). As for the nozzle if it is old probably just want to get a new one. I bought some E3D nozzles, they are premium price but I have to say they are noticeably better. The nozzle has more brass mass up front so I think it puts the heat where it needs to be.
Had this many times the nozzle is done after a while the end closes and shaped differently. If you have a jet cleaner you can try cleaning it but i usually just replace them when this happens and it will work again.
