Mobile navigation issue in Repository

Hi, I have a Repository setup that works very satisfying on tablet and desktop. On a mobile screen though… the navigation becomes a ‘burger’-button
But, when clicking on it the menu (dropdown) opens for a blimp (half a second) and then closes again… what could this be?
Repository 2.4.2. / RWC 9.2.1. / Stacks 5.1.2. / Foundry 2.4.5. / Blankstrap 5.3.3.

Which theme are you using for the repository page?

Foundry 2

Foundry 2 is not supported. Only Foundry 3. Switch to Blankstrap theme.

OK, thanx Jannis.
I might migrate the whole project to Foundry 3.
This was an earlier build F2 project that I was dusting off ;-)