Cheogsh.wad

It probably won't.
So the only think I'd advise you - run wad on Zandronum. Yesterday I checked blue skullkey's whereabouts there, and it was on the platform.

And yeah, a friendly info, BTW.
Seems the whole Cheogsh trilogy is suffering of that GZDoom problem.
Cheogsh 2, for example - in the New City of Damned, there's a specific teleporter that sends you to a cage, somewhere in the darkness, where you must fend off ghauts and flying skulls. And instead of sending you INTO the cage, teleporter gives you a sh*tload of [censored], sending you UNDER the cage, meaning instand gib death for player. Nice, eh?
Also, Realms of Cheogsh suffer of the same problem - in the City of Despair map, that is in space.

So basically, there are 2 possible outcomes: 1) using noclip + fly; 2) switch on Zandronum. I wish there could have been 3) GZDoom FINALLY works properly with that, but... y'know...

I temporarily put on God mode, then took it off after the cutscene ended. That works.

Wow, I remember playing this wad. Dood stuff.

Wow... Inspiring design