Puppet 5.5.19 breaks puppetserver

Puppet Version: 5.5.19
Puppet Server Version: 5.3.12
OS Name/Version: CentOS Linux release 7.7.1908 (Core)

After upgrading puppet (agent) to 5.5.19 (on the server) and restarting puppetserver, all nodes receive the default manifest (i.e. no config). There are no warnings/errors in puppetserver's output and I don't know what to provide here. Downgrading puppet (agent) to 5.5.18 (on the server) resolves the problem.

The clients (other agents) can run 5.5.19 just fine, it's just the server's agent version that must be downgraded for the puppetserver to function.

Desired Behavior:

Upgrading puppet (agent) to 5.5.19 shouldn't break puppetserver.

Actual Behavior:

Upgrading puppet (agent) to 5.5.19 breaks puppetserver.