With RM active, my new Jetpack Portfolio custom posts lead to a 404

Hi, I’ve noticed a previous post in this forum with the same issue, which didn’t have a clear outcome, as the user simply disappeared.

I’ve been using the latest RM version, with no issues so far. As soon as I added my first portfolio post (using Jetpack custom ‘projects’ post type), I’ve noticed two things:

1) Once published, the post permalink would lead to a 404 page.
2) Going back to the posts list, the post becomes “Auto Draft” even if I hit ‘publish’ before.

Things I already tried (to no avail):

1. Disabling all the plugins and re-enabling one by one: RankMath was the culprit.
2. Disabling Jetpack portfolio custom post type and creating one by myself as a custom plug-in: nothing changed, same error behaviour.
3. Confirming the permalinks at each change.
4. Purging the site cache and cleaning my browser’s multiple times.
5. Rolled back RankMath to a previous version

I must point out that this issue never happened with normal posts.

Jetpack can’t be the issue because, as I said, I configured a brand new custom post type on my own, replicating the exact same problem.

Finally, I already checked the conflicts with Site Health. Nothing to report, all good.

Hope I can solve it because I really like RankMath!

Thank you.
Silvia