So I've been working on this for few days and I made a house and terrain in my file a few days ago. Today I made a Phonebooth collection which is working fine with hide on and off. But the collections I made a couple days ago aren't visible in the 3D viewport with hide off even though they're present in the outliner.
Here i have both Phonebooth and Terrain with visibility turned off, but only Phonebooth is visible. Even the camera and lights are invisible: