2.9 UI is broken, seems to loop between user intro and machiens pages endlessly

[webteam-app]

Bug originally filed by bladernr at https://bugs.launchpad.net/bugs/1915087

We just did a fresh MAAS install of 2.9 from the snap in a LXD container for the cert lab. I logged in using our default user account and created a personal account for myself. I then logged in using my personal account. The first thing that I should see is the intro stuff, and what I actually got was a lot of pain.
On log in, I got the machines list with no tabs to navigate. At the top the only options were "skip", my user account, and "Log out".

Skip doesn't seem to do anything at, clicking it does nothing. I clicked my user account and tried pulling in my ssh keys from launchpad. This resulted in an endless cycle of going between a blank page for l/user/intro and a populated page for /machines/ until I finally clicked my account again, returning me.

I created two user accounts, and both displayed exactly the same behaviour.

maas 2.9.1-9153-g.66318f531 11322 2.9/stable canonical✓ -
maas-cli 0.6.5 13 latest/stable canonical✓ -

See the attached video that demonstrates the issue.

also note, this is a snap. So obviously any sort of modifications and debugging is nigh impossible. And we cannot just delete the snap and start over, this is a production machine, unfortunately. So we'd like to work to resolve this in 2.9.1.