The essence of this. There is a bot (django -> gunicorn -> nginx -> debian 9 -> dedicated server with 24 Cores 64GB of RAM). The server receives about 100 requests per minute, then colback stops taking. A suspicion that something from the chain above the limit the requests per IP. IPtables is not installed. the configs of nginx no restrictions. What else can limit the connections per IP?
talking about iptables-save and see if there are rules limiting your queries
to exclude nginx helmet queries directly to gunicorn measured result
monitor the number of connections
watch the logs for too many open files