Problem with registration app on iphone ipad

1 - On Iphone, Ipad, We should automatically log in at the end of the registration of "nextcloud talk" with the app "registration" (https://github.com/nextcloud/registration) installed on the server (via regular apps install).

2 - The registration process stay blocked at the "loading" page (end of the registration). We have to kill the app and load again (then, it can take 1-2 min before the log menu appear ! )
The team of the registration app (Closed issue #297) tell me that it doesn't come from their application.

3 - Nextcloud 20.0.8; MySQL version "5.7.33"; behind a NAT livebox (port 443 + 80 open); installed with snap on ubuntu

Does it come form the snap configuration ? or from my firewall ? or from sturn that is not configured ?

Here are the logs I found:

Warning:

{"reqId":"VCWB373BAQ3z8RTKeMmq","level":2,"time":"2021-04-14T19:43:16+00:00","remoteAddr":"86.229.57.136","user":"--","app":"core","method":"GET","url":"/index.php/csrftoken","message":"Renewing session token failed","userAgent":"iPhone (Nextcloud Talk)","version":"20.0.8.1","id":"607b0d2140283"}

Fatal:

{"reqId":"XsUt3h43ezrz5GhUYanu","level":4,"time":"2021-04-12T18:00:56+00:00","remoteAddr":"86.229.57.136","user":"herve","app":"webdav","method":"PROPFIND","url":"/remote.php/dav/files/herve/","message":{"Exception":"Sabre\DAV\Exception\ServiceUnavailable","Message":"Système en mode maintenance.","Code":0,"Trace":[{"file":"/snap/nextcloud/27089/htdocs/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"checkMaintenanceMode","class":"OCA\DAV\Connector\Sabre\MaintenancePlugin","type":"->","args":[{"class":"Sabre\HTTP\Request"},{"class":"Sabre\HTTP\Response"}]},{"file":"/snap/nextcloud/27089/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":458,"function":"emit","class":"Sabre\DAV\Server","type":"->","args":["beforeMethod:PROPFIND",[{"class":"Sabre\HTTP\Request"},{"class":"Sabre\HTTP\Response"}]]},{"file":"/snap/nextcloud/27089/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":251,"function":"invokeMethod","class":"Sabre\DAV\Server","type":"->","args":[{"class":"Sabre\HTTP\Request"},{"class":"Sabre\HTTP\Response"}]},{"file":"/snap/nextcloud/27089/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":319,"function":"start","class":"Sabre\DAV\Server","type":"->","args":[]},{"file":"/snap/nextcloud/27089/htdocs/apps/dav/lib/Server.php","line":332,"function":"exec","class":"Sabre\DAV\Server","type":"->","args":[]},{"file":"/snap/nextcloud/27089/htdocs/apps/dav/appinfo/v2/remote.php","line":35,"function":"exec","class":"OCA\DAV\Server","type":"->","args":[]},{"file":"/snap/nextcloud/27089/htdocs/remote.php","line":167,"args":["/snap/nextcloud/27089/htdocs/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/snap/nextcloud/27089/htdocs/apps/dav/lib/Connector/Sabre/MaintenancePlugin.php","Line":85,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Macintosh) mirall/3.1.3git (build 4850) (Nextcloud)","version":"20.0.8.1","id":"607b0d21402e2"}

Error:

{"reqId":"SfuOcj7813COM7vzAjRT","level":3,"time":"2021-04-11T15:46:50+00:00","remoteAddr":"86.229.57.136","user":"Celine","app":"index","method":"GET","url":"/index.php/login/v2/grant","message":{"Exception":"Exception","Message":"Argument 1 passed to OC\Core\Controller\ClientFlowLoginV2Controller::grantPage() must be of the type string, null given, called in /snap/nextcloud/27089/htdocs/lib/private/AppFramework/Http/Dispatcher.php on line 169","Code":0,"Trace":[{"file":"/snap/nextcloud/27089/htdocs/lib/private/AppFramework/App.php","line":152,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->","args":[{"class":"OC\Core\Controller\ClientFlowLoginV2Controller"},"grantPage"]},{"file":"/snap/nextcloud/27089/htdocs/lib/private/Route/Router.php","line":309,"function":"main","class":"OC\AppFramework\App","type":"::","args":["OC\Core\Controller\ClientFlowLoginV2Controller","grantPage",{"class":"OC\AppFramework\DependencyInjection\DIContainer"},{"_route":"core.ClientFlowLoginV2.grantPage"}]},{"file":"/snap/nextcloud/27089/htdocs/lib/base.php","line":1008,"function":"match","class":"OC\Route\Router","type":"->","args":["/login/v2/grant"]},{"file":"/snap/nextcloud/27089/htdocs/index.php","line":37,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/snap/nextcloud/27089/htdocs/lib/private/AppFramework/Http/Dispatcher.php","Line":110,"Previous":{"Exception":"TypeError","Message":"Argument 1 passed to OC\Core\Controller\ClientFlowLoginV2Controller::grantPage() must be of the type string, null given, called in /snap/nextcloud/27089/htdocs/lib/private/AppFramework/Http/Dispatcher.php on line 169","Code":0,"Trace":[{"file":"/snap/nextcloud/27089/htdocs/lib/private/AppFramework/Http/Dispatcher.php","line":169,"function":"grantPage","class":"OC\Core\Controller\ClientFlowLoginV2Controller","type":"->","args":[null]},{"file":"/snap/nextcloud/27089/htdocs/lib/private/AppFramework/Http/Dispatcher.php","line":100,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->","args":[{"class":"OC\Core\Controller\ClientFlowLoginV2Controller"},"grantPage"]},{"file":"/snap/nextcloud/27089/htdocs/lib/private/AppFramework/App.php","line":152,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->","args":[{"class":"OC\Core\Controller\ClientFlowLoginV2Controller"},"grantPage"]},{"file":"/snap/nextcloud/27089/htdocs/lib/private/Route/Router.php","line":309,"function":"main","class":"OC\AppFramework\App","type":"::","args":["OC\Core\Controller\ClientFlowLoginV2Controller","grantPage",{"class":"OC\AppFramework\DependencyInjection\DIContainer"},{"_route":"core.ClientFlowLoginV2.grantPage"}]},{"file":"/snap/nextcloud/27089/htdocs/lib/base.php","line":1008,"function":"match","class":"OC\Route\Router","type":"->","args":["/login/v2/grant"]},{"file":"/snap/nextcloud/27089/htdocs/index.php","line":37,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/snap/nextcloud/27089/htdocs/core/Controller/ClientFlowLoginV2Controller.php","Line":153},"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:87.0) Gecko/20100101 Firefox/87.0","version":"20.0.8.1","id":"607b0d21408c0"}

Start by reproducing the iPhone/iPad registration flow against the reported Nextcloud 20.0.8 setup, then compare the /index.php/csrftoken and /index.php/login/v2/grant errors with the iOS app behavior. The issue is done when registration no longer remains on the loading screen and the app proceeds to login automatically, with the responsible component and a reproducible test or fix identified.