If you have specified one of your Regular Expressions to be used as a search criterion, and nothing is being found, and you 'know' there should be something found, it may be due to a Regular Expression compile error.
MCS just 'ignores' regex compile errors, and moves on, returning nothing.
MCS assumes that you have previously tested your regexes before trying to use them.
To easily test your Regular Expressions, go to
https://pythex.org/ and test them there. If one is invalid, you will receive an error message. You could then tune it until it works for you, then copy and paste it back into the MCS Regular Expressions Settings Tab.
Another testing resource to use is:
https://regex101.com/#python.
DaltonST