[solved] Windows client can't connect anymore

Hi
Since I migrated from the docker linuxserver image to the official nextcloud one, I have a lot of issues with the connections.
For a reason I don’t know, my windows client (v3.1.1) has been disconnected last night from my server (my account on the servers has been disabled twice in 2 days but I don’t understand why, maybe it’s linked to the connection problem of the windows client)
Anyway, when I try to reconnect, I’m redirected to the web page where I click to “se connecter” (sorry in French)


then I get redirected to this screen where I click on “authorize access”:

but it runs forever and in the client I get that error
image

In the nexcloud logs, I get login failed errors but they don’t seem to be syncronized with the connections from the client:
[core] Warning: Login failed: ‘olivier’ (Remote IP: ‘192.168.1.8’)

GET /remote.php/webdav/
from 192.168.1.8 at 2021-01-23T10:05:58+00:00

and in the http logs, I have this kind of traces:

192.168.1.8 - - [23/Jan/2021:11:07:56 +0000] "POST /index.php/login/v2 HTTP/1.1" 200 1138 "-" "Bagheera (Desktop Client - Windows)"
192.168.1.8 - - [23/Jan/2021:11:07:58 +0000] "GET /index.php/login/v2/flow/51EjPjgYEGVfdpQxdjIU4Sc0dYiNVsevwVwdhEPQOqD3O8wTSfs6aZNc3zSmFYCYEEpH1tcC700rqxRGHPYR84O86KujSPHQlpwwh67Awnsa9HcxLHyGj9yDADNDxNTL HTTP/1.1" 303 845 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:07:58 +0000] "GET /index.php/login/v2/flow HTTP/1.1" 200 6444 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:07:58 +0000] "GET /apps/theming/image/background?v=4 HTTP/1.1" 404 715 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:07:58 +0000] "GET /apps/theming/image/logo?v=4 HTTP/1.1" 404 714 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:00 +0000] "GET /index.php/login/v2/grant?stateToken=osMahSgbtIeBFDqpUFVnPebaLyYzb9RuQbVLBlJUPFTXyeI1I6rJP3SK7B2STkuD HTTP/1.1" 200 6404 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:00 +0000] "GET /core/js/login/grant.js?v=1d694a93-4 HTTP/1.1" 200 855 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:03 +0000] "GET /core/img/loading-small-dark.gif HTTP/1.1" 200 2348 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:07:54 +0000] "GET /index.php/apps/logreader/poll?lastReqId=GpEYx0IXwiOUsgJmyCmg HTTP/1.1" 200 827 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:12 +0000] "PUT /index.php/apps/user_status/heartbeat HTTP/1.1" 204 723 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:13 +0000] "GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1" 304 286 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:17 +0000] "GET /ocs/v2.php/apps/user_status/api/v1/user_status HTTP/1.1" 200 956 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:14 +0000] "GET /index.php/apps/logreader/poll?lastReqId=GpEYx0IXwiOUsgJmyCmg HTTP/1.1" 200 827 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"
192.168.1.8 - - [23/Jan/2021:11:08:43 +0000] "GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1" 304 286 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:84.0) Gecko/20100101 Firefox/84.0"

I can’t find anything related to login/v2/poll

Nextcloud version (eg, 20.0.5): 20.0.5.2
Operating system and version (eg, Ubuntu 20.04): latest official docker on raspbian buster
Apache or nginx version (eg, Apache 2.4.25): 2.4.38
PHP version (eg, 7.4): 7.4.14

Is this the first time you’ve seen this error? (Y/N): Y

Unable to grant access for sync client through Login Flow V2 solved the issue