Uploading large files to the server through nginx reverse proxy does not work

I have a problem: there is a site, with nginx and php-fpm. It works with sending files of any size (in accordance with the restrictions of nginx and php). However, only files in 1-2MB + - are sent through the return, more - no. It's clear that I also increased max_body_size on the reverse proxy, however, for some reason, sending does not occur. And the problem is only with mobile devices - it works on a PC. I don't know where else to dig.