Issue with trying to adjust the exports Settings in Lightroom Mobile

Hello,

I have a very weird problem when trying to export pictires in Lightroom Mobile. I can't change the settings: everytime I try they always revert back to the following: picture quality at 80%, custom size. 
I am stuck with those settings and I have absolutely no possibility to change them
I emptied the cache, unistall and reinstall the application without any success. 

What can I do to solve the problem?

THanks in advance for your help

With Kind Regards

Alain