Why are some clients getting a 501 error after making this minor change in the nginx configuration file?

Question

I recently made a very small change in my Nginx configuration file and for some reason now some users (but not all) are experiencing a 501 error. I can't figure out what might be causing it. I've even restarted the Nginx server but that did not help. The worst part is that I am not able to replicate the 501 error on my end.

The only thing that I changed is I added the client_max_body_size parameter. Can anyone help? Thanks in advance!

location /api/microservices/process_data {
    client_max_body_size 100M;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-NginX-Proxy true;
    proxy_pass http://api_servers/process_data;
    proxy_ssl_session_reuse off;
    proxy_set_header Host $http_host;
    proxy_redirect off;
}