The plugin DOES work with 4.0, right?
Yes.
When I try to access the dashboard for the #2 site, I get the dashboard for the #1 site.
When I try to access the dashboard for the #3-#5 sites (unmapped) I also get the dashboard for the #1 site.
Since you have the same issue on all subsites (mapped or not). The simple way to eliminate DM from troubleshooting is remove it from your install until you get sites 3-5 working.
Anyone?
@bloggy2013 - what I suggested you check in my previous response to you was in your client/customer's DNS vs your webserver.