I was doing a run and took my hands off the keyboard to check my phone after I got into an elevator. 30 seconds later, the elevator hadn't moved. I looked around and jumped and all of a sudden, boom, it started moving. I repeated this on a few more.

Is there some kind of trick I should be doing after entering one to trigger it?

Ive noticed this but not sure what happens. I just got in the habit of going all the way and touching the back wall of the elevator and it seems to fix the issue

yes in some elevators are the triggers a bit messed up for example in 18 and 05, if you want to be really safe though just get to the back of every elevator, at the beginning, and you should be fine.

If you have more questions, in the Portal Speedrun Discord are many awesome people that are happy to help you.

i stand in the middle of the ele and dont have an issue, not all the way back or forward though

I can't remember all of them, but 18 and 5 come to mind. I recorded one instance in chamber 5. Skip over the first few minutes of trash speedrunning please.

It only happens at the chambers where you have to wait for dialouge, so only 05 and 18, just don't stand at the front of ele to fix it.

this actually happens to me as well in basically every elevator. stand in the middle and move.