ConversationView shows progress wheel over messages on Nexus 5X

I noticed this on the Nexus 5X (Android 8.1) with current master (25b8932c) and can reliably reproduce it there, but I can't reproduce it on the Moto G 4G running the same code.

Steps to reproduce:

• Sign into Briar
• Open a private conversation containing some messages
• Turn the screen off and on again, or press the home button and then resume Briar from recent apps
• The progress wheel appears over the top of the messages and doesn't disappear