The first issue you spoke about has been quoted below.
Bear in mind, as easy as the green-coloured pop-ups are with predicted responses can make life, all instruction options can be found in the controller GUI. For pushbacks, for example, just click [Pushback approved] and you’ll be guided through an immediate pushback acceptance and one that directs them to a particular runway. I haven’t experienced this issue before, but I hope this thought-out solution will be useful for you. Your other issue, I have…
I haven’t actually had this issue in a while. When it did happen, my internet connection would be strong and the usual culprit factors were all in order. When I did experience it, I’d restart my game and retry. In the event this failed, I’d go to a different airport and control there for a minute. By “control,” I really do mean: log in and log out. Then, after returning to the originally desired airport, all would be well. This is a bit of a crude resolution but it always worked for me and I do understand how there can be a rush to get to EGLL and other busy airports first.
I hope the workarounds (not perfect solutions) find some use. I’d invite anyone else to possibly build on my thoughts to find a proper fix!