after going through the portal in the overworld the entrance to the dungeon is invisible, there are clearly blocks that aren't rendering. but if you walk forward enough you can see the rest of the dungeon. Note the entrance/portal in the overworld seems to render without issue. The issue only occurs when going through the portal.

It seems like an object occlusion issue because collision still works; and the bounding boxes of the invisible blocks near the entrance still render. Additionally particle effects like the ones around the entrance/exit portal still render; but the
Additionally if you walk past the invisible entrance section the rest of the dungeon will render. If you turn around to look in the direction you came from you will see nothing but the skybox.

This is not a client side issue because this occurred in a server with a party of 3, all users reported the same issue.
I am running 1.8.0 of the mine cells mod.

Hey, are you playing on some modpack? This has happened to me before, but only on FantasyMC, and nowhere else...
I'd appreciate a modlist (or even better the log file from when this happened)

Edit: also, it'd be best to update to Mine Cells 1.8.2, because it fixes a few critical bugs