Things break. Latest example: my Ebelin powder brush. It didn’t exactly break but the glue wasn’t strong enough to hold the handle in place. A good reason to return your newly bought brush, however the easiest way is to glue things back in place and it doesn’t damage the brush or makes is less usable. It is also a way to “repair” wiggly brushes.
Mostly after you’ve washed the brush a couple of times and didn’t exactly follow the rules of how to hold a brush during the process and afterwards, the handle gets loose. I say: break’em apart. As you can see down below, the handle doesn’t break, it is simply the glue that you separate from it. However, be gentle and do it slow.
Once they are apart, glue them back together with a general superglue. Be careful to place the glue only at the handle’s end or inside the hull. That way you won’t see any glue residues and the brush looks perfectly new.