While shooting photos there are two ways to check if the photos are uploading.
Option 1. Upload icon
On the right top of the app you see multiple icons. One of them is the 'upload' icon (see image below). When photos are uploading, this icon turns green, and when the photos are uploaded the icon turns grey again.
Whenever the app has a problem with uploading the photos, this icon is red.
Option 2. Upload queue
Whenever you have shot photos and you upload them, you will see the amount of photos is showing in the upload queue (see image below). This number indicates how many photos are uploading. If you for example took 2 photos, you will first see a '2' here. While your photos are uploading this '2', goes to '1' and when the photos are uploaded a green check mark appears.
Whenever the app has problems uploading the photos, you will notice that a number is showing in the upload queue. The more photos the app could not upload, the higher this number is. To see what photos have failed to upload you can press 'queue' on the right bottom.
It's important for photographers to keep track of this while they are taking photos. The sooner you notice a problem with uploading, the faster the problem can be solved.