Stall can come from technique, the filter, the grind, the coffee… pretty much anything in the process. What type of pourover brewer are you using and, generally speaking, what's your recipe look like? Specifically, how long is the entire brew taking? And how is the coffee? To a degree most brews will slow down as they progress.
If you're always stalling with different speed filters and grinds and coffees, it's likely technique. If you're not taking some steps to make sure you agitate the coffee throughout the process, the brew can stall as the coffee settles into the bottom of the brewer.
Different filters do often run at different flow rates. That's fairly well documented across the internet, but if you'd like some breakdowns on a specific filter I'm happy to link you to some. There are extremely fast filters that some people love. But the common filters can all produce good coffee with little to no stalling.
Your grinder could be producing enough fines that you'll stall regardless of grind size (within reason) for a given filter. Fines aren't really something you can control well, short of replacing a grinder. Grinding coarser can help a bit, and then you can control other things (more pours, less aggressive technique) to keep the brew rate even.