For those who are reading this and still can’t find a solution for the same problem, I followed this post and everything is working correctly now :https://forum.arongranberg.com/t/turn-based-grid-difficulties/7037/4?u=natalia14
In my case, to avoid Units from being blocked by their own occupancy, I used Dictionary instead of HashSet in order to save my Units as values. Then check whether the Unit that is occupying the detected node is NOT the same as the walking Unit.