PHP Warning: Invalid argument supplied for foreach()

Actually there is check on the file list, but probably in your system the glob function is returning false, as if there was an error.

I’ll change the checking code.

Thank you!

You could use this tool for debugging, monitoring your plugin development:
https://github.com/johnbillion/query-monitor
and this one is specially for profiling/speed/load
https://github.com/szepeviktor/whats-running
with these in mind:
https://github.com/szepeviktor/WPHW/blob/master/wp-entry-points.md