Abnormal delays in download

[Pierre Couderc]

I am trying to download a 12M pdf file and it takes more than 4 minutes 
with http nginx while it takes a few seconds with scp.

I have asked detailed log here https://paste.debian.net/1206029/

I see timeouts but I am not able to interpret them correctly.

nginx is in lxd container in a nearly not used  server (htop load 
average 0.08 ...).

I use nearly defaut debian configuration of nginx.

Thanks for any help.