Kong and NGINX keep giving timeouts

Can someone help me?
I am having a load test by JMETER which sends requests to KONG API GATWAY and then from KONG to NGINX.

*kong_1 | 2023/08/04 10:39:52 [error] 1114#0: 206369 upstream timed out (110: Connection timed out) while reading response header from upstream, client:, server: kong, request: “POST /explain_shap/image HTTP/1.1”, upstream: “http://nginxserver:80/explain_shap/image”, host: “XX.XX.XX.XX:8000”

Nginx logs: - - [04/Aug/2023:10:39:52 +0000] “POST /explain_shap/image HTTP/1.1” 499 0 “-” “Apache-HttpClient/4.5.13 (Java/1.8.0_381)”

The problem is I get the following errors on Kong and NGINX.
Of course I also put large value for timeouts in kong panel and also defined large timeout on Nginx configuration but still …