Unable to connect to Nextcloud from iOS app

Our users are experiencing the following problem : impossibility to connect to our Nextcloud instance from iphone iOS client app.

After logging in, that is typing their login and password, they get an error page telling :
Access forbidden
CSRF check failed

We’re on Nextcloud 14.0.3 + LDAP accounts
Any idea ?

Sincerely yours,

Same here on Nextcloud 15.0.4 with local accounts