Presumably you have a startup script for this, and these days that would typically be a systemd type of script.  So the question would be: what does your systemd script to in order to start up pydecnet?  Did you specify a log file?  What's in the log file?

Also: did you upgrade from V1.0 or from T1.1?  There are some config differences between 1.0 and 1.1, described in the README.txt file.  The one that could prevent startup is this one, introduced during the T1.1 beta cycle:

f. The --api and --insecure-api switches on the "http" configuration
line have been removed.  Instead, API control is via a new "api"
line.  See doc/config.txt for details.

One more possibility: did you switch to a newer Python?  If so, did you install any library packages needed for your config?  For example, if you want to start pydecnet with the --daemon switch you have to have python-daemon installed on whatever python version you're now running.  Anything you install with "pip" -- any of those optional Python packages -- is installed for a particular version, whichever is the default Python version at that time or the specific one you referred to.  For example "pip3.10 install ..." will install something for your python3.10; it won't be seen by any other python version you might have installed.