3 phones 1 screen --> different results

[Phoenix]

I have one screen with only webview. I want to show my users a picture so I link to a picture.

https://startit.at/ menue/brot.PNG (I made a space within the link so you can see the link)

Problem:
I tested it on 3 phones. 1 iOS/2 Android devices. It works for 1 iOS and 1 Android phone. But it does NOT work for the third Android phone.

Background info:

1. It worked before/last week
2. If I enter a website link it works
3. I deleted the cache but it did not change something
4. iPhone 5C and Galaxy 7 work. LG X power does not work

Can someone help me please?