Hi Jean-Pierre,
Firstly, please try and post your questions in a new thread of your own and not in one started by another user, this saves on confusion and cross posting with the original starter of the thread.
Your issue could be down to how you have set up the redirect within Webplus and shouldn't really be covered here because it is Webplus related and not a template issue, however, looking at your code you have this for the redirect
wpRedirectMobile('http://www.kallemoeietriatlon.be/mobile/index.html',5000);
I have no idea why you have 5000 set within the parameter of the code, normally if selecting to only redirect if a mobile is used, the code would be set like this for example
wpRedirectMobile('http://www.kallemoeietriatlon.be/mobile/index.html',0);
A lot of users have found that the redirect isn't very good from within Webplus itself, therefore, have a read of the following thread and see if that helps resolve your problem
http://seriftemplates.com/forum/topic/redirect-to-mobile-site
Just make sure if using the above, you delete the redirect you have created via Webplus and only use the file and code supplied from the thread above.
Hope this helps but please try and keep questions via this forum, template only and if you need help with Webplus itself, have a look over here - https://community.serif.com/forum -