It does not matter whether you have zero potential somewhere in your circuit. The main point is that you have a potential difference between A and B. Current will flow between A and B split over all possible paths, in your case you have three paths: 1-2-5, 1-4-5, 1-4-3-2-5.

The network of resistors can be replaced by an equivalent resistance which you correctly calculated to be 2R/5.

If you reshape the funny circuit in your question you will see that it is completely equivalent to the following more familiar circuit

It does not matter whether you have the same potential somewhere in your circuit. The main point is that you have a potential difference between A and B. Current will flow between A and B split over all possible paths, in your case you have three paths: 1-2-5, 1-4-5, 1-4-3-2-5.

The network of resistors can be replaced by an equivalent resistance which you correctly calculated to be 2R/5.

If you reshape the funny circuit in your question you will see that it is completely equivalent to the following more familiar circuit