Hey Marije, alles goed? :)
Maybe the problem lies in the fact that you use the same words often. Maybe the search is finding all the records with a matching word?
Tell us a little more about your structure.
All these checkbox values, are that all on one field?
The checkbox get their values from a list
Do you mean you used a list of custom values?
And how are the numbers (M10-13) in this list? Are they separated?