Multiple Themes in multisite

I am the original author, and I don’t recall any issues with multisite installations. But memory fades, especially since I generally advised people to reorganize their site to use Multisite to get around any issues I could not solve with the Multiple Themes plugin. In other words, splitting a site into two multisite sites, but making it look like one site to the visitor.

I’m not in a position to support the plugin, but it has been adopted out, almost two years ago, to someone who can support it. You will, however, have to use his support forum. Details are here: https://wordpress.org/support/topic/important-support-for-multiple-themes-has-moved/