MBdoc - see:
https://coffeetime.freeflarum.com/d/719-condensation-on-lelit-elizabeth
Could you take a few photos of the inside of the machine, so we can inspect the connections visually?
With the top of, after machine has heated up, with both boilers on, can you video so we can see/hear anything? (Video via YouTube, make the video unlisted and paste the link here).
Welcome to the forum.