Sure you could, friend, I have 400 mods running lol.
The most possible answer is you downloaded the mods with the game running, and Steam on default doesn't allow something downloading while a game is running; exit the game and go to steam download page and check the download status.
Another possible condition is that your mods are not version compatible, check if all the mods says 1.5, and when finding mods tick the 1.5 on the right bar. But normally it will show as red in the mod menu instead of disappearing.
If both doesn't work, plz post a screenshot of the in game mod menu and the subscripted items in the workshop.
The most possible answer is you downloaded the mods with the game running, and Steam on default doesn't allow something downloading while a game is running; exit the game and go to steam download page and check the download status.
Another possible condition is that your mods are not version compatible, check if all the mods says 1.5, and when finding mods tick the 1.5 on the right bar. But normally it will show as red in the mod menu instead of disappearing.
If both doesn't work, plz post a screenshot of the in game mod menu and the subscripted items in the workshop.