basically this means you don't have the Deluxe Battle Kit installed, it was supposed to auto rescue the error but i guess that's not working properly, you can either install the Deluxe Battle Kit, or go into the VMS_Battle_Handler file and delete the line of code "setBattleRule("noBag")"...
Plugin is not tested on the ebdx, it currently only supports DBK, i will be testing further those desync issues you listed, also, the plugin doesnt't have a version 2.09, did you mean version 2.09 of the ebdx? If so then they probably changed something in how battles are handled on that plugin...
This is very weird, i wasnt able to trigger any desyncs when switching pokémon here on my computer, can you upload a video recreating the exact steps to trigger this issue?
Also, about the not being able to battle on your own computer, i'll be honest and say i didn't really understand your...