The affected site is espace-temps.ch which should be a subset of mag-si.ch.
I tried modifying the dns of the parked domain (free) and adding the domain to mag-si.ch (payed option)
My hosting and registrar is Infomaniak network (www.infomaniak.ch)
Could it be because of a security plugin? I have word fence and i theme security shared on the wordpress multi-site network. It is a domain based network and it works perfectly with si-sr.mag-si.ch and news.mag-si.ch.
Thank you very much for your help