Getting exactly the same issue. Completely locks up Unity for several minutes on start up. Once menu become responsive again if I then just click scroll wheel to move down page locks up Unity again. Wait several minutes and if lucky menus become responsive again but page has not moved. Try to scroll down again and same issue completely locking up Unity yet again. Whilst never liked new v2 of store now it renders Unity useless as can't scroll down to even click on revert to old store. Only solution is do a force exit via Task Manager. Just tried to see if Unity working whilst been writing this message and still locked up and haven't tried to do anything for 10 minutes.