It's not especially wise - and may be against local code - to put a 30A breaker on a line with a 20A outlet. Similarly, I wouldn't put a 20A breaker on a line with a 15A outlet.
If your lines run close to each other or in the same conduit, it is possible that one is affecting the other.
If your lines run close to each other or in the same conduit, it is possible that one is affecting the other.