Diminished Flow Rate Capability

Hi all.

I've been printing with ease all these times, limiting my flow rate to around 15cm3/s. I calculated it with a formula of (layer height x extrusion width x speed) CMIIW.
I have a 0.5mm nozzle and running on 200°C PLA.
It should be fine and it has been fine most of the time.
I just got clicks from my drive gear while extruding however. It's like, i've been running for weeks, then it happens. Usually I just do the atomic method by cold pulling the filament (no contaminant detected) or by poking the nozzle with thin wire. Sometimes the problem disappears and sometimes not. I'm not really sure what the exact cause of this.
Did I miss something?

maybe your stepper driver is set too low?

You did not miss much
Depending on the filament you can get a build up of filament in some areas.
If that happens inside the nozzle or melting chamber the stuff can go old, hard and brittle.
Usually it still comes out fine but the stuff that got too bad will partially colg the nozzle hole.
Had it a few times that all the poking did not help, or only for half a print.
After literally taking the entire hotend apart and cleaning it all properly I was fine for another three rolls.
I also noticed that some colors are less sensitive when it comes to the black goo building up.
Pigmented filament like white or some yellow types are bad and it is best to do a proper clean if there are extrusion problems.
Natural, red, blue, green never gave me any troubles in that regard.
Worst I had so far was a set of two PLA rolls, one black, the other purple.
Both were contaminated with small fibre parts.
So I could print a few meter with no issues at all, then a bit of fibre comes and the nozzle was so blocked that I had to burn it out