Photoshop hangs on return to working state after execution completion of an external exporter plugin

"You have identified that the lag occures after the completion of the process of the plugin and have reasonable facts to make the statement."  Can you provide the details what is going on what are the facts? You provided no details about your plug-in its design,  its or its operation etc. We do not know if your statement is correct may be it is we have no facts to go on. Have you tried toggling Photoshop UI pallets off while the plug-in runs so Photoshop UI palette elements will not need to be updated the often speeds up processing of Plug-ins and scripts.

// I use Photoshop UI with Photoshop toolbar and option bar visible and toggle Panel via Shift+Tab
// This Toggle_panels function works like Photoshop's Shift+Tabe shortcut
if (ScriptUI.environment.keyboardState.ctrlKey||ScriptUI.environment.keyboardState.altKey|| ScriptUI.environment.keyboardState.shiftKey) Toggle_panels("Off");
else Toggle_panels("On");

function Toggle_panels(how) {
	if (how=="Off" & panels_visible() ) { 
		togglePalettes(); 
		TglWindowOptions();    
		TglWindowTools();      
		//alert("Palettes were Visible");
		}
	if (how=="On" & !panels_visible() ) { 
		togglePalettes(); 
		}
}

//alert(panels_visible()?"Panels are visible":"Panels are hidden"); 
function panels_visible() { // Thanks r-bin
    try {
		var r = new ActionReference();
        r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("panelList"));
        r.putEnumerated(stringIDToTypeID("application"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum"));
        var list = executeActionGet(r).getList(stringIDToTypeID("panelList"));  
        var viz = false;  
        for (var i = 0; i < list.count; i++) {        
            var obj = list.getObjectValue(i);
            var id = obj.getString(stringIDToTypeID("ID"));
            // skip some panels if shift+tab was pressed
            if (id == "panelid.static.toolbar") continue; // skip tool panel
            if (id == "panelid.static.options") continue; // skip options panel
            if (obj.getBoolean(stringIDToTypeID("visible"))) 
                {
                viz = true;
                break;
                }
            }
        return viz; 
        }
    catch (e) { throw(e); }
}

function TglWindowOptions() {
    var desc1 = new ActionDescriptor();
    var ref1 = new ActionReference();
    ref1.putEnumerated(app.charIDToTypeID('Mn  '), app.charIDToTypeID('MnIt'), app.charIDToTypeID('TglO'));
    desc1.putReference(app.charIDToTypeID('null'), ref1);
    executeAction(app.charIDToTypeID('slct'), desc1, DialogModes.NO);
}

function TglWindowTools() {
    var desc1 = new ActionDescriptor();
    var ref1 = new ActionReference();
    ref1.putEnumerated(app.charIDToTypeID('Mn  '), app.charIDToTypeID('MnIt'), app.charIDToTypeID('TglT'));
    desc1.putReference(app.charIDToTypeID('null'), ref1);
    executeAction(app.charIDToTypeID('slct'), desc1, DialogModes.NO);
}