Played Mystery Heroes, got Orisa with the Fortify and Charged Javelin perks. Whenever I held right-click for the javelin, the animation would play some disjointed frames and then the arm would disappear, making it difficult to tell when the ability was fully charged.
I have not encountered this issue in regular modes, so I suspect it is linked to spawning in with the Charged Javelin perk (and so is specific to the Mystery Heroes mode).