Hi phmsp901,
I believe you. I have one paid Fusion 360 account (Early Adopter, had been a paid user for two years, going into third year from Jan 2016. Total about four years now). A few days' ago I also signed up another Fusion account using the Mac App Store because it is needed in my country of residence. A Mac App Store version was installed in an older Apple Air just for purchasing the license. I then started the "Original Web Downloaded Version of Fusion 360" in my quad core I7 Mac Mini. I then signed out of the original account. The Sign In dialog box came out, I entered the second paid ID and the screen flickered quite a bit and went crazy. Luckily my Mac did not stop working but Fusion could not be used. I could Force Quit it. I tried to do the same thing on the other Mac on the same desk in the same network. The same thing happened. I used the old trick this time. I uninstalled Fusion from both machines using "Uninstall Fusion app", I then clicked "Finder", selected Go To Folder, entered "~/Library", then selected "Application Support" and deleted the whole "AutoDesk" Folder. A new installation from Fusion's Web (this site in fact) was done and this time I could sign in and out of both accounts. But one thing also very strange; The TEXT selections of the top manual bar were there when Fusion was started with one account. When I signed out, entered a second paid ID Fusion started again but the TEXT selections of the Top Manual Bar disappeared. Only one TEXT selection remained there. I think it was the word "Fusion". I closed and restarted the program the manual bar TEXT appeared again.
I believe you had hit a bug in Fusion that only people signing in and out of different ID's would experienced. I think you did the right thing. Use a different machine for Fusion. If you wanted to use the original machine, uninstall, delete AutoDesk folder and download again. But beware, if you had other AutoDesk programs installed you cannot delete the entire AutoDesk folder. You will have to delete the related Fusion Files in the"AutoDesk" folder. I only had Fusion and SketchBook Pro Mac version so I could delete the Folder. Mac App Store apps are installed in a different manner.
I Hope this reply gives you a little more confidence in this program.
Have a nice week!