@] BR via Nginx :
Idea coming right out of the blue: have you given a thought on compiling
nginx (+ gradually modules) with valgrind? ​You should know pretty quickly
if something is wrong.​

Thanks for this idea which can really improve the eng process...

Brotli seems the main suspected issue

Anoop just told me :
**the reload is changed to USR1 for stats////

I will upgrade soon, this should dramatically reduce the issue to 0 nearly...