One of the possible solutions I think, can you try?
function afterrender(sender, eOpts)
{
sender.getSummaryStrs = function(sender) {
var
me = sender,
rStr = '',
sFeature = me.getView().findFeature('summary');
if (sFeature && sFeature.getSummaryBar()) {
sFeature.getSummaryBar().ariaEl.select('.x-grid-cell-inner').elements.forEach(function(el) {
if (el.innerHTML != ' ') {
rStr += el.innerHTML.replace(/ /g, ' ') + ','
}
})
}
return rStr.replace(/.$/, "");
};
if (sender.pagingBar) {
sender.pagingBar.add({
xtype: "tbtext",
text: "",
id: sender.id + "_summaryStr"
});
sender.getStore().on('datachanged', function() {
if (Ext.get(sender.id + "_summaryStr")) {
Ext.get(sender.id + "_summaryStr").setHtml(sender.getSummaryStrs(sender))
}
});
}
}