debian – How to find which process sent a HUP signal to my node.js process?

Every Monday at 9AM UTC something sends a HUP signal to my node.js process (and I think HUP is being sent to all processes, not just mine). How do I find which process sent the HUP signal to my program? My program has a HUP handler that makes it restart (to reload config), so every Monday at 9AM, my production stack restarts on its own (but keeps running, so all is good, it’s just super annoying).

I have a feeling it’s systemd doing it, I just don’t know which part of systemd is doing it. Any ideas?

It’s a Debian 11.7 installation.