system status page is empty, with no javascript errors
I upgraded from CiviCRM 5.14.1 to 5.15.1. My system status page doesn't show anything. The "main content" part of the page source looks like this:
<div ng-app="crmApp">
<div ng-view></div>
</div>
However, there are no javascript errors in the console. To try to resolve it, I tried "cleanup caches" and also a menu rebuild, and flushing caches in Drupal. This is running with Drupal 8.7.5.
I don't know if it's related, but I have another problem that showed up at the same time. When I first log in, going to CiviCRM shows an error page with the message:
Received unknown parameter: api_version
Reloading the page makes the error go away, making it seem like something to do with having the right cookies set, perhaps?
How can I debug this further?