Cell data and Wi-Fi networks are not always reliable. It's not rare to be connected to Wi-Fi or have full bars for data, and the connection is still very slow or non-existent. Still being able to use other apps or browse websites on your phone does not mean you have a stable connection. Apps and websites usually cache information and do not require any sort of upload bandwidth to use.
The two most common instances when a connection issue is causing trouble in the Time To Pet Mobile App are viewing the schedule and completing an event/uploading a visit report:
There are a couple of things you can try:
Turn off Wi-Fi on your device and toggle airplane mode on and off
Restart the phone, and close out all other applications that are running on the device
Reduce the size of the pictures that are being uploaded. Use less than three images and ensure each iimage's size is under 100kb