Why does this happen?
This issue commonly occurs if you're primarily using a phone/tablet to transfer pictures to your Google Drive account. If data is an available method to connect to the internet (as is the case with most phones/tablets), the default setting on Drive is to only transfer files when you're connected to WiFi. Otherwise your file transfers will be "put on hold" until a WiFi connection becomes available.
How can I fix it?
Open up the Google Drive app on your device and select the 3 stacked horizontal lines on the top left, then scroll down and select Settings. At the bottom of the Settings page, turn off the Data Usage setting "Transfer files only over WiFi". This will allow your pictures to be transferred whether you have a WiFi connection available or not.
Please use the following attachment for a quick walkthrough on sharing Google Drive links when using Apple and Android devices.