+1 to the previous comments; also, the rounds in my case were not even been making it out of the mag, i.e., they were getting stuck IN the mag, horizontally.. between the breech face and the inside of the front of the magazine tube. This may or may not be your situation. Take another look when it happens again and see whether it's truly hung up on the ramp.

But one other thing to add. The magazines that came with mine were absolutely FILTHY inside and I would recommend taking them apart and cleaning them regardless. I don't think it's a good idea to put oil in there as it can attract/retain gunk and end up binding them up worse, unless you make sure to dry them very well afterwards.

Meanwhile, the mags can be a little tricky to disassemble but in the link I posted earlier there are disassembly instructions. Of course, be careful to RE-assemble them 100% correctly.