I've not officiated at anything like that level for many years now, and in my day I only had the occasional higher profile game (fourth official D2, linesman at Macc Town for FA Cup preliminary round, Central League etc.) So I am not familiar with the recent phenomenon of allowing play to continue for a few seconds before a linesman raises his flag. I see it as giving the attacking team false hope, before cruelly snatching it back from them. In my day, we would flag an offside, and if play developed in a certain way, the referee would wave down the flag and continue the game.
I agree that the three offsides and the penalty decision were given very quickly, almost as if they were a pre-determined outcome to certain events. So, given the three offside goals in the game at WHL, Clattenburg might have instructed, "OK, let's not have any more offside goals today. If there is anything remotely marginal, I want an immediate flag from you." Hence no possibility of another controversial offside goal, but plenty of scope for incorrect offside decisions being made.
This of course is contrary to FA directives, which I understand are to err on the side of the attacking team, so the marginals should not be flagged.
The worst decision of the two games against Spurs was obviously the penalty given to Spurs. But the second worst decision was Kane's goal at WHL, which was scored following their free kick. As it was from a free kick, there is absolutely no excuse for the linesman to get that wrong. He can see the kicker running up to take the free kick, and he only has to glance along the line of defence to see two players clearly offside by some distance at the point the ball was kicked. One of them, Kane, then scores from the rebound. This has gone relatively unnoticed (the focus has been on other bad decisions). But this was a linesman failing to identify an offside from the easiest possible set of circumstances. It is hard to believe this was a genuine mistake by that official.