It’s supposed to be fixed on the client side (IJPL-171075), but the split-mode may be a different thing.
I tested my monolithic paid plugins in a splited IDE, and I faced two issues:
the license checks partially worked (edit: I tested again, it did not work at all). I think this was normal, as my plugins are not supposed to support remote IDEs (like Gateway).
some Swing UI elements were not correctly displayed (I have some settings panels with things like JetBrains’ EditorTextField fields), even when the plugin is installed on the host side.
I will try to create a sample plugin based on v2 plugin descriptor and see what happens with the license checks and Swing.