Why is upstream latency increasing when my custom plugins are enabled?

Hello! I am running into a weird issue in Kong 2.7 where I see no considerable Kong Proxy Latency, but I notice an importante Kong Upstream Latency. This is not what it looks like from the upstream perspective, everything seems to be answered quickly.

This is DBless mode, default mem_cache_size value.

if my high-CPU-consuming custom plugins are disabled then I do not see the upstream latency at all. Could it be that some plugins are affecting the upstream latency in Kong?

I think I may be running into a CPU throttling issue, but what it is totally weird is that the Kong Proxy latency is always stable (~5ms) even when the upstream latency that is detected by Kong is around 1sec.