Do the pages have one, exactly one tag assigned? I am asking because by default the pages can have multiple tags, separated by comma - so in your filter you would need to list the actual value saved for given page in given field - and the tags can be added in various order so there are many, many possible combinations. I am not sure what is your exact goal, but maybe you are looking for data filtering and not searching. I just explained the difference (in the backend, for the front end user it might be the same) in this thread. So, maybe you want to use that approach instead as in this case, creating a custom filter which will generate WHERE condition with LIKE '%some text%'
instead of search filter which is using logical AND might be much easier to maintain.