I’m having the same problem too.
2.3.1 running locally is fine, but 2.3.2 running on the server omits the “Thumbnail” option. I have emailed the host, and they insist that GD is running. I’ve not got PodPress installed (which some threads cite as the culprit).
Image sizes are fine (tested the same image with both versions)
Any ideas gratefully received.
Thanks
JL