Cast bar not showing up on focus target

I am not sure if this is a known bug but sometimes I don't see a cast bar on the focus target when it's casting a spell. It can get a bit annoying when doing SCOB Turn 1 when the fight get's really hectic. Sometimes I don't notice Rafflesia casting Blight because the cast bar isn't showing up. I don't have any TTL issues and my ping is between 70-80ms.

Ive seen this happen on other mobs in other instances as well. So it is not limited to just coil. Perhaps it is a lag issue or a genuine bug.