Sounds like a mag fit issue. I'd suggest buying a Chinese 10 round internal/intergral/factory mag and running that. I do own a few Tapco 20 rounders, and have never had an issue with them. But until you know how your rifle cycles using a true SKS magazine, the factory 10 rounder, I would not suspect the rifle being the problem.
Not bashing tapco 20 rounders. They are all I use besides factory 10 round mags. Just saying that aftermarket mags may be the cause of your issue.