I installed WPMU Dev Dashboard just now on my Wordpress Multisite (v.4.5.2). It seems to install ok and I see the link for WPMU DEV in the sidebar of my network dashboard. It is network activated without any problem. However, when I click on the WPMU DEV link in the sidebar to set it up I see the setup screen for a split second, then it redirects to a 404 page. Then I'm just kinda dead in the water.
I contacted my host (SiteGround) and started a live chat with them and they said the best thing to do first would be to contact you guys since it's a paid plugin - so here I am
I also searched your support forum (and Google per your Good Support Ticket tutorial) for "WPMU DEV Dashboard 404". Scanning the support forum titles that came back I didn't see anything that helped. I did find a couple of items using the Google search method but the discussions didn't cover what I'm experiencing so I decided to start a support ticket.
Can you assist? Since I cannot grant you access via your dashboard plugin, I have created a user for you to go in and repeat the problem (which is repeatable). Please let me know the best way to transmit the credentials to you.
The issue can be recreated by going to My Sites > Network Admin > Dashboard, then clicking the WPMU DEV link in the left sidebar. It will flash the WPMU DEV screen for just a second then redirect to a 404 page.
Please let me know what else I can do to help you assist me. Thanks in advance. Hope you're doing well.