Size problems when adding new images to gallery

Help! After the most recent update of Jetpack the gallery on my portfolio site started behaving oddly. If I add a new image to my gallery, it creates this huge image! I just want it to look like the other images. ??

Here’s what I’ve tried so far:
– I’ve tried deleting the gallery and just creating a new one.
– I’ve used firebug to check out the code. All I can see is that this image is 634x634px, while the rest are all 209x209px.
– I’ve tried disabling my other plugins to see if there was a conflict.
– Temporarily assigning a different static homepage to edit the gallery, and then changing my static homepage back to “portfolio”.

None of this has solved my problem.

Also, I should mention that I’ve created my theme using Underscores, Shape 2 and the original Shape Theme. It’s the first theme that I’ve created, so it’s entirely possible that this is all due to a newbie mistake. ??

Any help is GREATLY appreciated! The link to my portfolio site is below:
https://www.stephleece.ca/