Back in my 35mm days I used Leica lenses/filters and read a Leitz recommendation that it's easy to remove a stuck filter by using the thumb & index finger to pinch the filter rim at one location and turn. Seemed obvious this was to avoid distorting its round shape into an oval, creating additional friction on the threads. So, I've always used this technique and it's always worked. It's likely that all threaded filters have rims that protrude from the glass far enough to grasp in this manner.