Grey transparent bar on PDF files

[ArnoDeG]

I work in a company where we use a lot of samsung tablets and phones.
Lately some people have been having problems with PDF's.
As you can see in the picture there is a grey bar on top of the screen, this only appears when reading PDF's.
We have tried installing a different pdf reader but the result is the same.
Resetting to factory settings also doesn't work.

Anyone got any ideas for a fix ?
Can't seem to really find anything on the internet.

 

[Dannydet]

Does this happen for any type of pdf, single page also?
What pdf readers have you tried?

 

[Dannydet]

What happens when you click on the document tab along the top?

 

[ArnoDeG]

Does this happen for any type of pdf, single page also?
What pdf readers have you tried?

Any PDF, single page as well

Does this happen for any type of pdf, single page also?
What pdf readers have you tried?

Also single paper PDF's and the built in PDF reader ofcourse, Adobe and Simple PDF Reader

 

[ArnoDeG]

What happens when you click on the document tab along the top?

No Idea, I'll find out

 

[svim]

So just for context, is that grey bar showing in the same position when you scroll a page up and down, or does it also move when you scroll a page up and down?
Is that grey bar only occur on those Samsung devices, or when you view the same affected PDF file on a different mobile device or a computer there's no such problem?