Hi Scholto,
I just tried it on a test environment with the latest versions of both plugins, but I was able to save and edit the yoast seof fields. There are no errors indicating issues on the console, nor on the server log.
I suspect it might be a browser/server cache related issue. Can you please try clearing your browser cache and try it again?
If nothing changes, I will have to check the issue directly, as I’m not able to re-crate it. In that case, please edit your ticket to add temporary log-in and FTP details as well, thank you!