Did you mix well before printing?
I’ve noticed Black resin in particular, left for a while in a tank, develops a thick, jelly-like film that clumps up on the end of your scraper when you start to mix it. If you mix long enough it eventually “dissolves” back into the liquid to develop a normal consistency.
As for cartridges, if I haven’t used one in a couple months I’ll give it a rigorous, 10 minute shake by hand before putting it in the printer (or leave it for a couple hours in a spinning rotisserie I made).
For less critical prints, I’ve also mixed the last of my old resin with newer, more fresh resin of the same type.