When you say “Thank you” to someone, the proper response is not “No problem”.
“Thank you” is said when you are appreciative of someones work or effort so responding with “no problem” really isn’t appropriate. A more appropriate response might be “you are welcome” or “glad I could be of service”.
Unfortunately, people have developed habits of responding in certain ways without regard for whether the response is correct or not.
While it might not be a problem, it doesn’t mean it’s an appropriate response.
Have a great day!