Since version 12 upgrade our customer and their editors have been experiencing an issue with the page tree where the actions such as delete and move are not reflected immediately on the user interface. This causes them to repeat the action only to get an error message. I inspected the issue and it seems like the delete action triggers a call to /EPiServer/cms/Stores/contentstructure/ and the response of this request in turn triggers a refresh on the page tree.
However, when testing in Slow 3G throttle mode this HTTP call took 12 seconds for me to complete in integration environment. The page tree does not show any spinners or whatsoever during this period to give an indication to editors that something is happening in the background.
I think a simple spinner would solve this issue.