The adjective muable has as its core sense ‘changeable’. However, the sense ‘in motion, mobile’ seems to have developed as well, most likely under the influence of movable and moeble. It is only this secondary that is attested as a nun- comnpound.
(
c.1200; MS: s.xiiiin
) A la parfin li ciels, li soleilz, la lune, les esteiles e iceles choses qui ore sunt muables, lores serunt en pais e nun muables
98.78
nunmuable (c.1200)