This morning I put a cartridge of tough resin in my Form2 for the first time in a few months, and my print stalled trying to fill the tray before printing. I pulled the cartridge out and tried the bite valve by hand and sure enough, nothing. Cap was open, but no resin flowed. I had already shaken the cartridge for minutes, so as a last resort I poured the cartridge out into a cup. What came out was both liquid resin and huge clumps of goopy resin.
This tough cartridge is the same age as other durable resin I have (in fact I checked another tough cartridge of the same age, same problem). So this may be unique to tough. The cartridges are stored in a dark cool place. One of them was sealed (new).
Now it may be that these are beyond the recommended shelf life (they’re V3), but if you have any tough V3+ and having trouble dispensing, this may be something to check.
I was able to stir the resin back into liquid form and refill the cartridge. (The print is going now, and may fail…)