[RCD] Invalid or Expired Session

We've had sporadic reports of expired or invalid sessions from users. They'll have a roundcube page open, possibly other tabs, too, then click on compose or on an email message and be presented with a login screen that says the session is invalid or expired.

We're thinking it's possibly related to js getting stalled or the keep_alive not being run due to the page being 'busy' for any other reason, but reproducing the behavior, let alone diagnosing it, has been difficult.

Our sessions are in mysql and have a length of 10min, keep_alive runs every 60s.

Has anyone else had reports like this?