Nginx proxy_pass docker client_body_buffer_size=0 gives http 400


I recently upgraded from seafile community server 6.x to seafile pro 7.0.7 with official container.
Actually, it didn;t work so I recreated a new seafile dataset from sratch.
The docker container is listening to http internal 80 (default) and external 8000, and public traffic come through nginx https + letsenctypt via 443. Nothing fancy.

On the host machine, the listen server, the location, and nginx proxy_pass parameters haven’t changed when I created the new container. The host nginx proxy_pass has the usual set of parameters you would expect: no max body size, no timeout, no buffer, etc.

What i don’t understand is why I cannot connect with the client/drive when the host proxy_pass has client_body_buffer_size=0 ? I can connect to the web UI perfectly.
Client trying to connect gives these 4x lines in the access log:

“POST /api2/auth-token/ HTTP/1.1” 400

I had a hard time pinpointing the parameter at fault and it is client_body_buffer_size=0. Since i am using the official container with yaml and port 443 disabled, everything is default in the container.

My problem is solved but it doesn’t make sense that setting this parameter client_body_buffer_size would result in total inability to connect?? I want to know because if I don’t, it’s like I set that up by chance and have not understood nothing.

client_body_buffer_size=0 is supposed to avoid writting buffer larger that 16k (64bits OS) on disk.

Any idea?
below is the location definition i use for seafile:

location ^~ / {
  include         global/server/proxy_params-nolimit.conf;
  proxy_pass      h t t p://;
  proxy_redirect  h t t p:// /;
 # access_log  off;

below is the proxy_params-nolimit.conf:

proxy_redirect          off;
proxy_set_header        Host                $host;
proxy_set_header        X-Forwarded-Host    $host;
proxy_set_header        X-Forwarded-Server  $host;
proxy_set_header        X-Real-IP           $remote_addr;

proxy_set_header        X-Forwarded-For     $proxy_add_x_forwarded_for;

client_max_body_size    0;
client_body_timeout     90;
## client_body_buffer_size 0; will prevent login to seafile, for some reason
#client_body_buffer_size 0;
proxy_connect_timeout  36000s;
proxy_read_timeout  36000s;
proxy_send_timeout  36000s;
send_timeout  36000s;
proxy_buffering off;
proxy_request_buffering off;