Nice reading:
https://help.nextcloud.com/t/101-split-brain-dns-split-horizon/202579
https://help.nextcloud.com/t/101-network-domain-and-dns/201882
https://help.nextcloud.com/t/101-self-hosting-information-for-beginners/187015
Other topic is even well known issue. Do some reading on github issue discussions desktop clients android or ios.
Being french is no excuse anymore 
.