I'm having trouble with a V11 installation (running on an t3.medium EC2 server - 2 Vcpus, 4 GB ram) where the web client will occasionally hang (several times a day) with the spinning wheel during a simple action (saving a record or navigating to another page) and not be able to reconnect until I restart the server.  I've let it run for several minutes and it still won't connect.

I've checked the odoo-server.log and there never seems to be an error coinciding with the hangs, but there is often a  large number of bus.bus records being deleted (odoo.models.unlink) by User #1 at the same time.  For example, there might be four or five log entries with hundreds or even thousands of records deleted.

In fact, lately the server appears to spend most of it's time deleting records.  Is this a normal process to be happening in the background?

This same system has been running very smoothly for several years now until the last few weeks.  The only significant change I can think of that has happened around the time when it started is a Ubuntu update (running 16.04 LTS).

Can anyone suggest how I might begin troubleshooting the problem?