Multi-db Plugin Database Not Found

Hi, I understand that the multi-db plugin is decommissioned but it is the only alternative we have yet to find for our needs. We have a multisite with over 4000 sites and we desperately need to split the database.

We did so using the plugin and we have a database not found error. That being said all of the information and sites are distributed throughout 17 databases(the 17th being the global data base).

They just don't seem to be sending information. Is there anything that anybody recommends? We desperately need this or something similar to work as our site won't hold up with many more added blogs.