@KaiserRuben Your problem sounds familiar. One earlier case was this thread. It is long so I will summarize here.
Do you by chance have perl enabled? If so, try disabling it, restart nginx and see if that allows the renew.
Why? A conflict with nginx can result using the nginx plug-in as after it makes the temp changes to your nginx conf it reloads it using SIGHUP. That's fine but if that fails it will start nginx but not using systemd. This creates an nginx that cannot be managed by systemd and the two nginx fight each other for ports leading to the symptom you saw.
Now, various things can cause the SIGHUP to fail. A common one is not having nginx running before doing the renew. Of course then the sighup will fail. You said nginx was running so likely not your cause.
I mention perl only because that explained the SEGV that the nginx sighup was failing with in the thread I linked to. We would have to dig through your system logs like we did in this linked thread. But, it would be a quick test if you had perl just to disable it.
A work-around is to use webroot as that avoids the nginx plug-in altogether. Webroot uses your running nginx as it is.