ok so I figured it out ( I think)
mendix loads certain elements offscreen in the div “mx-incubator mx-offscreen”
this div doesnt play well with elements that have a fixed class such as mobile headers.
fixed it with:
.mx-incubator.mx-offscreen{
display: none;
}
Not me, but do you only experience this in 7.23.0 or also in previous versions?