Search for members doesn’t show everyone

A few days ago I  was trying to give certain people certain roles (mobile) but I realised not everyone showed up when I filtered for a role. I filtered for the moderator role and gave everyone who showed up another role but when I looked at the side bar there were more people. I think this was because they were offline at the time but I’m not sure. This is really annoying because I didn’t know how many people have the role. If it is that it only shows online people or if it just isn’t working, (again I was on mobile) then I think that should be changed or be able to switch it to show online, offline or everyone.