Hi josefk
The problem comes from the data built for template package only, the team is exporting this package again.
In the meantime, you can go to Backend of your site >> Extensions >> Templates >> open JA Blockk template style >> Navigation section >> Edit >> turn off the 'Build Mega Menu' option like this:
Or when you build megamenu, you can simply edit / load an existing module on your site, it will work well then.
Regards