I overwrote the jQuery with the old version, that fixed it.

According to the latest package.json for Bootstrap 4.4.1, the jQuery version needs to be at least 1.9.1 and less than 3

I think we introduced a new bug by updating to ImpressCMS 1.4 - the newer version of jQuery is not compatible with the version of Bootstrap used in the theme. The result is the navigation menu does not work for mobile devices, or even when you desktop browser emulates a mobile device.

Looks like it is fixed now. And my temporary issue with the forum that stopped me from posting has gone as well. 

Now we may have something - each forum has its own setting for allowing HTML. This one didn't allow, until now.

Let's see what happens.