I had that problem at one point. If you don't have all of the DLC, then mods that require it will crash. I haven't seen any that want CoTW yet, but check if You Have To Name The Expansion Pack is installed. It won't automatically download and has to be "purchased" from the store page.

I got the meltdown mod to work by manual download. So it must have been a different one.

Yes, one of the mods you downloaded either needs a DLC youdo not have. Or the mod itself is bugged. You should check the descriptions of all the mods you installed.