Crashes for client at ID verification stage

Hi,

Once our documentss are sent to our cleint and they recive a n email and then a text messgae. It then ask for their ID and a selfie. Many (but not all) clients crach at the selfie stage and cant go any further. This has been on iphones and android (we think). We have also tested ourselves and find its hit/miss. Some of us it works on an iphone and some it doesn't. 

We send client application forms out for completion, signing and ID verification and this is urgent