Shoulder shrugging and head tilting to the shoulder

[DadDuties]

My 8.5 months son has been doing this shoulder shrug and head tilt to one shoulder or the other for the past couple of weeks. Some old posts here have pointed to teething or ear infection, however neither applies to him. He does this at random times and mostly when he’s sitting up, or when we’re holding him upright. We’ve read a lot about infantile spasm, could this be IS?

That’s not one I’ve come across before, sorry @DadDuties

An update for anyone who’d be following this in the future - we had an eeg and mri done and both came clear. The shrugging has stopped itself now, so we’re not sure what it was.