[BertieBark]

It used to happen every now and then but now it's getting more and more frequent.

I've tried giving the phone a 'technical tap' to try and free whatever's sticking but it didn't help. Any suggestions?

[Nabkawe5]

Do you mean that your view finder is shaking? like you can't get a still shot even though your phone is completely still?
If so this is magnetic interference, OIS works by utilizing a magnetic ball that holds the sensor which sometimes can act up for seemingly no reason.

I think the best solution is not to hit the phone but instead shut it off for few minutes and then try again.

[BertieBark]

Yes it shakes, it's more of a violent jerking and clicking than a soft shaking if that makes sense?