Can you check if in case this is a bug on the plugin code?

Both plugins are using Composer, am I right?
You wrote to the support that “it’s as if it’s adding a piece of the WPLM execution time to Patchstack” and that’s 100% true: if multiple plugins use Composer, only one instance of it will be loaded. And as WordPress loads Patchstack before WPLM, it is its instance that will be used to load WPLM classes as well. Composer is a great tool for developer, but it’s a pain in the butt when it comes to profiling a WordPress site with multiple plugins using it.
Didn’t the profiler display a notice below the graph about that?

Thanks for verifying that once again! We’ll try troubleshooting then by keeping these Composer using plugins turned on one by one.

You can also use Freesoul Deactivate Plugins to deactivate plugins while profiling. The developer has a post on their blog about that: https://freesoul-deactivate-plugins.com/profile-your-website-with-code-profiler-and-freesoul-deactivate-plugins/

Thanks for the advice!