I have the same problem. I use the QBO app using Desktop View. I use Google Chrome. I've cleared the cache, used MS Edge and even tried on a whole other computer. Still can't get to Custom Reports tab unless I deselect Desktop View. I have found a work-around. Change from Desktop View. Got down to Reports and select Custom Reports. When the Custom Reports menu appears, switch back to Desktop View. Go down to +Add a shortcut at bottom of left menu and click. You may have to click twice. Enter Custom Reports in Bookmark box and Save. It is now in your Shortcuts menu.