I don't know what causes it, but it's been reported as fixed in the progress page (
http://ulm.illwinter.com/dom3/dom3progress.html) and I managed to get a mod to work by disabling all mods except the one I wanted to try. It could be that Tomb Kings triggers it even if no other mods are enabled, and I don't know if you can do anything but wait for the next patch in that case.