i have the same issue, it seems to be that either another recent MCC update broke this mod, or something else happened

yep. load screen loads indefinitely. :(

Having the same issue, normal HALO CE campaign loads. Tried verifying game files, resubbing to the mod, and currently trying redownloading HALO CE game content.

I was able to get it to work, I removed all installed game content for all the HALOs and only downloaded HALO CE campaign and multiplayer. After it finished I restarted the game and it worked.

I found a solution to fix this issue folks.

First go to halo then settings next to controlls layout, then click on properties, and it should take you too general settings.. scroll down till you see launch option.. click it and select "play halo: MCC ANTI-CHEAT DISABLED (Mods and limited services)" after selecting that option launch the game and enjoy

i had this issue, then i went and made double sure i had multiplayer and halo ce downloadable content installed, turns out i did not have the multiplayer for halo 1, i clicked that/ toggled that and got it downloaded, i noticed another button for the mod itself under a tab called workshop, and clicked it/ toggled it, it was under a different tab for workshop as opposed to the DLC. then i ran the game and it worked. i hope this helps. also at some point i restarted my computer. good luck