Yes, I can also confirm this behaviour, which has existed for as long as I’ve been using the website. It only seems to affect the image viewer in the Identify dialog. I use Firefox, and there is no console output.
It seems to happen most reliably when there are multiple images. The first image usually seems to zoom in and out as normal via repeated clicking, but after moving to the next image, it zooms in and out once and then stops working. And the same goes for all the other images. However, if I go back to the first image, the zoom in/out usually starts working again - but only once for each image. This behaviour is not entirely constistent, though, so it may be necessary to try several different observations in order to see it. Once the behaviour is seen for a particular observation, though, it always seems to be repeatable for it. So far, I have never seen the behaviour with observations that only have one image (but I haven’t done any exhaustive testing).
My hunch is that there’s some kind of weird caching issue, perhaps linked to the size of the images being loaded.