LMS URL SpringerLink assignment intermittently opens in Public layer

## Bug report form
Reported via Slack convo https://hypothes-is.slack.com/archives/C2BLQDKHA/p1667327866121689
### Steps to reproduce
1. Create LMS URL assignment for https://link.springer.com/article/10.1007/s42438-022-00302-7
- Canvas assignment here: https://hypothesis.instructure.com/courses/258/assignments/3701
2. Launch assignment until you see sidebar load with Public layer, rather than course group. In my testing it seems to happen 1/10 tries or so.

### Additional details
HAR file here: https://drive.google.com/file/d/1_o3sA9o7d-Vj1QudSUd6ufECElvNG6_x/view?usp=sharing