looks like a bug in WebFloatingPanel.js

Code:
set_pbHideOnBlur : function(bVal){
    if(this._aFocusCatchers){
        this._aFocusCatchers.forEach(function(eEl){
            eL.tabIndex = (bVal ? 0 : -1);
        });
    }
},
the eL should be eEl

you can try adding this to your index.html file as a workaround (warning untested)

Code:
        <script>
//   Fix for WebFloatingPanel pbHideOnBlur
if(df.pnDataFlexVersion == 19.1){
df.WebFloatingPanel.prototype.set_pbHideOnBlur = function(bVal){
    if(this._aFocusCatchers){
        this._aFocusCatchers.forEach(function(eEl){
            eEl.tabIndex = (bVal ? 0 : -1);
        });
    }
};
    
}    
    </script>