Node.js Elastic Beanstalk - Can't choose Amazon Linux 2 on platform version change, even though it's supported

Hi,

I'm currently running Node.js 12 running on 64bit Amazon Linux 2/5.6.1 (retired) without any change to the selected Node.js minor version, and would like to upgrade to Node.js 18 LTS. There is a supported platform version of Node.js 18 AL2 version 5.8.8 (link), but for some reason I can't choose it and the upgrade modal shows only Amazon Linux 2023:

The thing is that the "Platform version" dropdown also changes every time I open the window - one time showing only 6.0.3 as single option, and sometimes showing 5.x options without 6.x.

I'd appreciate any help. Thanks!