Ionic 4 virtual scroll is blank when scrolling programmatically


I was able to scroll to letter “Q” programatically using “positionForItem(index)”
However after a few clicks the virtual scroll becomes white/blank.
It will only redraw when scrolling up or down.
I tried every possibile way to force redraw: zone, app.tick, markdirtytail, markdirty(0,all), etc.
Any idea if is it possible or is it a bug? => {
                .then(res => {
                    this.content.scrollToPoint(0, res - 50).then(res2 => {
                        //this.MainScroll.nativeElement.markDirty(0, this.allItems.length);