We posted a new game jam a few weeks ago, but it does not appear to be showing up on the main jams page, which makes it really difficult to find without a google search...

https://itch.io/jam/canada150game (page for the game jam)

https://itch.io/jams (main page for current/upcoming game jams)

We set this game jam to be "public," is there another possible reason it is not appearing on the jams list?

I published a Jam few days ago and it took two or three days to be listed in the page because of the time to review. Maybe something went wrong. Up to this post, you should contact the admins.
Hope you to solve as soon as possible!

We posted the jam over a week ago and it WAS in the list, but is now gone. Hmm.

We are having the same issue, jam was listed and showing and now is no longer on the list.

Reported this via the contact us page, but haven't heard anything back in a week. Any support avail from Itch?

Logged a bug:

https://github.com/itchio/itch.io/issues/630

Admins? Anyone? It's been weeks & we are unable to get support on this issue.

Rec'd a response (thanks):

We currently don't show jams that extend longer than 30 days on the calendar to prevent them from taking up a permanent spot. I've updated the gird of jams below the calendar show it though.