Are you properly diluting the fixer? The fixer normally comes as a concentrate, and you need to mix it with water.(posted 8570 days ago)Make sure that all the steps from developer to wash are at the same temperature. Temperature changes can lead to funny emulsion things.
What about your stop bath? Is it properly diluted? I actually mix my stop for film at 1/2 strength. Too strong a stop with some developers can lead to pin holes from gas formation in the emulsion. You don't even really need stop, plain water will work about as well. Try it.