sounds like you've got some crap in the nozzle.
Could be junk from filament or manufacturing fault (does happen).

2 ways to approach it.
1) buy new nozzles, few quid/bucks. This might just be me, but I always replace nozzles in pairs. Nozzles can rub across bits of print and i find that if you just replace one nozzle, they never match exactly.
2) try cleaning it out. guitar strings are good for this. I tried tiny metal drill bits - they tend to snap in the nozzle and make things worse.
If you've been using abs, soak it in acetone and then poke with the guitar strings (actually metal wire). If pla, heat and poke, also push a little filament in and pull it out. If lucky crap will stick to it. Cut end and repeat a few times.

I think I've been lucky only ever had one nozzle clog in 3 years.

Or, the right nozzle is not perfectly level with the left nozzle. Lots of advice for this in the forum.