Symfony version(s) affected: 4.4.*

Description
All deprecation notices are somehow being suppressed intermittently. Some symfony deprecation notices show up but none from my own app show up in the symfony toolbar. When I look at the logs there are no logs for php.INFO.

How to reproduce
config/packages/dev/monolog.yaml

monolog:
    handlers:
        main:
            type: rotating_file
            path: "%kernel.logs_dir%/%kernel.environment%.log"
            level: debug
            channels: ['!event']

Anywhere in src/

trigger_error('Something is deprecated.', E_USER_DEPRECATED);

Expected output in dev.log:

[YYYY-MM-DD hh:mm:ss] php.INFO: User Deprecated: Something is deprecated. {}[]

Actual output: nothing

Possible Solution
None that I'm aware.

Additional context
This all happened after I changed my configs from the Symfony 3 style to the Symfony 4 style.