In the solver, press the upper right button (step by step analysis, F2 button by head). In the bottom right corner you can now see the results of the current iteration. Press the button again and you'll get the results of the next iteration. Most probably there are some nodes where the current state is open, the previous state is closed. In the next iteration it will be the other way round. Change the +Y restraint for this node into a Y-restraint and run your analysis again.
If the occuring upward force in the Y restraint is not that large, you can say you've made a good model, even when you use a Y instead of a +Y restraint.