Are your mags standards, mid, or highcaps? And how many do you have that fail to "feed" all at the same time? If it is a mag issue and they are standards or mids, you can spray a small amount of silicone in the mag. Use the loading tool to excersise the spring to ensure an even coat and see what happens. If you do this your hop up will be effected untill you go through several mags. Also are you making sure that your mag is correctly positioned? I know but the hardest problems can have the simpliest answers. Because if it is not seating correctly the pin/lever that holds the bbs in the mag, will not be released to allow the bbs to enter the gun.
An easy way to see if your mag has a problem, load your mag as you normally do. THen manually press back the holding lever. You will either have a bunch of bbs all over the place (suggest doing that in a bag) or the spring will fail to push the bbs out.