The key to flow is trust. We don't flow when we don't trust others, their reactions, the outcomes, ourselves basically.
But then trust is all about ourselves. True others can step up and make the place a trusting or mistrusting space, but in the end it's all about you and how much you trust yourself.
When you trust yourself, you will find it easier to trust others and when you find it easier to trust others you will find it easier to be in flow and when you are in flow, you find it easier to be happier and work better.
When you are struggling with flow, look at who you are not trusting. Then look at yourself and ask why you are not able to trust yourself? Why you are not capable of earning their trust? Then work on yourself - your trust with yourself.