I've got a nice R&Co 0/3 brush I use for detail work on epic minis, recently it started to hook, as the brush is a semi-synthetic blend, I followed some advice from a quick google search and dipped the very tip of the brush into a mug of boiling water for 3-4 seconds, a quick reshape later and the hook was gone! I've now got my lovely fine detail brush back
just thought I'd share, if your beloved brush hooks, don't chuck it away or relegate it to drybrushing or basing, try dipping the very tip in some boiling water to soften the fibres and reshaping it
you're welcome!
oh and if all the bristles fall out, you dipped it in too far.... don't blame me...

AS IT MAY BE UNCLEAR ABOVE, DO NOT DIP THE WHOLE END OF THE BRUSH IN THE WATER, JUST THE 1-2MM THAT ARE HOOKED, MORE AND YOU RISK MELTING THE GLUE HOLDING THE BRISTLES IN