The “Contains” function currently only supports complete words (for example, “Peter” will return “Peter”, but “Pete” will return nothing). A more flexible search has been asked for on the board earlier, and the Bubble team has, if I remember correctly, said that this will probably be added at some point in the future, but they can’t commit to a date.
This thread takes up the same challenge, with some discussions on the new feature, and a possible (but complex) workaraound: