Client timeout when use-native-transport on Ubuntu is set to true

When running a Minecraft server with either the latest snapshot or 1.16.4, the client disconnects a few minutes after joining. Mobs will freeze in place for a few seconds before the client disconnects with usually a Connection reset by peer error (although I've sometimes gotten a message that simply says Disconnected, and one time I got kicked for "flying"). On the server, the server console will usually say something like:

%PLAYERNAME% lost connection: Timed out

I have tried OpenJDK 8, OpenJDK 11, and AdoptOpenJDK 8. I have tried disabling the firewall, which also did nothing. The only thing that seemed to fix it was setting use-native-transport in the server.properties to false. There, I was able to keep playing for an hour without any issues.