Others have reported this too, but I'm not sure what's causing it. My only guess is that you have another addon that's removing it, though I can't imagine why an addon would do that. Maybe some optimization tool from someone who doesn't know/care what they're doing?

Try opening the console (Shift+Esc) while playing the map and then entering these commands, one line at a time:
Doing this may give you some information on Lua code that's affecting the tram.

If that doesn't help, you'll have to temporarily disable everything else and then restart the game. If that fixes it, re-enable your addons in small groups until you find the one that causes it to happen again. Please let me know if you can find the source of the issue.

Adding on to this: I suspect that it could also be caused by a nextbot/chaser addon, as people started reporting this issue around the time that those addons went viral. Given how frequently this map and the tram pop up in the videos I've seen, it's possible that the author of such an addon deliberately broke or removed things to mess with players.

In any case, I'm willing to investigate the issue myself if you can share a collection of all the addons you're using (or at least the addons that were installed or updated in the last three months or so).