Open MS office files with other apps

Hi, I’m reporting the problem of a friend of mine that is using nextcloud on an iPad.
He complains that since the last client update, he’s able to open an excel file but he can’t scroll it nor visualize other sheets.
Is anybody experiencying similar problems?

I’m going to ask him more details like iOS version and what app is opening the .xls files.
Server side is nextcloud 10.0.1 on debian jessie.

Here are the details:
iOS 10.3.1 e DocsToGo

Ok, I can define better the problem now because I saw it my self:
when I open an excel file, it opens within nextcloud client.
It shows only the first sheet.
There’s no way to move to the other sheets.

On the iPad there’s the Docs To Go Premium app installed.
I could use it to open and edit the office files but there’s now way I can set nextcloud to do that.

Any help is appreciated.

Nextcloud 2.17.3
Docs To Go: 5.3.6
iOS 10.3.2.