When working on crafts occasionally I run into this (only on mobile so far, hint hint) issue. Virtually the entire designer stops responding.
I've noticed in career mode if you open the menu and tap the "career" button and close out of the career menu it can fix this, but that fix won't work for custom planetary systems.
https://www.mediafire.com/file/g6ohy8mrdna875e/screen-20240916-120655.mp4/file