Thanks Steven for your swift reply !

All software is update.
Indeed it seems to be the "internal browser of messenger" the cause.

Using the link via Mobile Safari works just fine.

I have reproduced the issue with your gallery

Sent link via messenger
Clic link in messenger.
(phone is held stand : vertical)
Thumbnails are displayed fine
Clic first pic
Tilt screen horizontal to display the picture larger (as its a horizontal one)
The picture and screen are as expected
Swipe to display next photo (still holding phone horizontal)
The picture and screen are as expected
Tilt screen vertical to display the picture larger (as its a vertical one)
-->> only a half screen is displayed.

Tilt back to get out of this "half screen".

So the issue is vertical photos can not be displayed in "large"

Screen shot attached

Hi all,

I wonder if someone has an idea for the strange issue I have just encountered.
In short, my gallery doesn't work as expected when accessed via a link sent in messenger

On my iPhone 6, when my gallery is opened via a link sent in messenger, there are issues.
- photos dont take whole display (landscape)
- vertical photos are displayed on a half page (once screen tilted) - (ie the vertical photo keeps the same size as when displayed with the screen in landscape mode)

It took me a moment to understand I was not "in safari" , but still in messenger.
Opening the same gallery, same phone, but via safari is fine.

best wishes to all