The Watchlist (English Wikipedia, Vector skin) displays a "View new changes since ..." prompt when new changes have been detected by the background Ajax thread.
This prompt is positioned with the area that is collapsed by the Hide button of the Active Filters panel.
This means that the prompt is hidden when the Active Filters panel is collapsed.
Move the prompt out of the area that is hidden by the collapse.
The following jQuery code is used in a user script to make a suitable correction to the layout:
x$ = $('.mw-rcfilters-ui-filterWrapperWidget-showNewChanges').detach();
$('.mw-rcfilters-ui-markSeenButtonWidget').parent().after(x$);
mw.util.addCSS(`
.mw-rcfilters-head {
min-height: 0em !important;
margin-bottom: 0em !important;
}
`);