Pictures resizing only sometimes

I would like my main post pictures to resize themselves to a square – which most of them are doing (310×310, and I’m not sure where those dimensions came from)…. but other are not resizing properly, and I’m not sure why my site it picking and choosing which ones to resize and which ones to ignore.

Here’s an example:
https://www.holestories.com/?s=budapest

Frist article picture is too big
Second article picture is fine (even though the original is even bigger)

Ideas?

Thanks!!