Their problem - one of many - is that 'bisexual' is the the B in LGBT+. But 'bisexual' was coined after 'heterosexual' and 'homosexual' when sexual attraction was universally understood to be based on biological sex
Now attraction is supposed to be based on gender not biological sex, but there's no such word as 'bigenderal' - or not yet
Lots of people use just 'bi'. Perhaps they need to dump 'semibisexual' and stick with 'semibi'.
(Which takes us back to Eric the Half a Bee.)