For years, every time I've opened the air pressure release valve at the top of my filter (in order to release air bubbles), it's violently spewed out water a few feet away. I understand this is normal.
About a week ago, I opened up the filter to drain it and clean the grid, and now, the release valve doesn't do that anymore; now it weakly dribbles water out of it.
But the pressure gauge on top of the air filter looks normal, which tells me the pressure inside is OK. The jets in the pool look normal. (I don't see air bubbles, and if I put my hand in front of them, they're definitely pumping water into the pool.)
Here's a video of me trying to open the air release valve: