[Worker0]
on output logged by a ScriptedImporterScriptedImporters run on Asset Import worker processes1). These importers can't be debugged normally with the Mono Debugger in Rider or Visual Studio. Breakpoints can be set, but will never be triggered, because the breakpoint is being set in the Editor process, not the Worker process.
Rider can connect to these worker processes manually if you want to debug them via “Attach To Unity Process…”.
[Worker0]
on output logged by a ScriptedImporter