I have started working on OnPremise after so many years and I have to understand one of the plugin that was not working in some scenarios. I have written good traces to understand the logic and deployed the plugin.
To my surprise, while testing no plugin trace logs were generating. I was little surprised for sometime and after checking the things slowly came to know that the Plugin Assembly was deployed on None mode(Not in Sandbox mode).
I have seen community discussion where people were saying the Plugin Trace Logs are not getting generated under None mode. Hope Microsoft will fix it soon.
For the time being, I have registered the plugin under Sandbox to get the trace.
Hope this helps.