[HarisF1]

I went and tested it on my camera with a 50mm lens as well as the same 35mm lens. It seems like the vibration was a product of both my handholding technique and some kind of resonance in the shutter/mirror mechanism. The issue manifests itself when I perch the camera on a hard surface (such as the edge of a window frame) where it's not 100% flat but rather pivoted. When I pressed the shutter down abruptly I was torquing the camera body slightly leading to a vibration at and around 1/100s. If I stabilise the camera properly (or press the shutter more gently) then the issue doesn't show up. SR settings don't seem to affect the problem, I was able to replicate the issue with SR on as well as off.

TL;DR: Incorrect technique amplifies the tiny bit of vibration in the camera, leading to blurred photos.

Thanks for the help guys.