Repeating "Session expired" (in development mode)

On master @ a3b73f2d8bbea147148a0c57d7d5474471c2acd1. I keep getting "Session expired" messages, including when I try to import (more) keys from a Ledger. Refreshing the browser doesn't help. Seeing this in both Safari and Chrome on macOS.

Some log:
```
[2022-02-18 17:50:13,282] INFO in _internal: 127.0.0.1 - - [18/Feb/2022 17:50:13] "POST /hwi/api/ HTTP/1.1" 200 -
[2022-02-18 17:50:15,553] ERROR in controller: CSRF Exception: 400 Bad Request: The CSRF session token is missing.
[2022-02-18 17:50:15,554] ERROR in controller: Traceback (most recent call last):
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask_wtf/csrf.py", line 256, in protect
validate_csrf(self._get_csrf_token())
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask_wtf/csrf.py", line 94, in validate_csrf
raise ValidationError('The CSRF session token is missing.')
wtforms.validators.ValidationError: The CSRF session token is missing.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask/app.py", line 1948, in full_dispatch_request
rv = self.preprocess_request()
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask/app.py", line 2242, in preprocess_request
rv = func()
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask_wtf/csrf.py", line 224, in csrf_protect
self.protect()
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask_wtf/csrf.py", line 259, in protect
self._error_response(e.args[0])
File "/Users/sjors/dev/specter-desktop/.env/lib/python3.8/site-packages/flask_wtf/csrf.py", line 302, in _error_response
raise CSRFError(reason)
flask_wtf.csrf.CSRFError: 400 Bad Request: The CSRF session token is missing.

[2022-02-18 17:50:15,555] ERROR in controller: '_AppCtxGlobals' object has no attribute 'start'
```