Can anyone explain this router log to me please? What are upnp subscribers?

@soliniai , what's your device model and current firmware?

The answer should be somewhat easy to deduce, at least if you are familiar with the layout of logs in general. Taking your time to do a Google search (or any other search engine), it should provide you with some basic information to make it easier to start reading the manual and learn more about the features.

I performed a Google search using the following part of your log sample:

miniupnpd: upnpevents_processfds: 0x8e3368, remove subscriber uuid:

Here is a link to the Google search:

https://www.google.com/search?q=miniupnpd%3A+upnpevents_processfds%3A+0x8e3368%2C+remove+subscriber+uuid%3A

I will post a couple of links below to sites where this type of log has been discussed already. It is recommended that you have got a modicum of knowledge about UPnP, at least knowing just a little bit about why they are used in the first place (as suggested in one of the linked posts).

[Github]

https://github.com/miniupnp/miniupnp/issues/306

The Github page is easy to read and contains the shortest explanation:

[miniupnp commented on May 18, 2018]one client requested event notification (through the SUBSCRIBE HTTP request)and connection to the notification http url timed out (the machine is probably turned-off :)

[Reddit]

https://www.reddit.com/r/HomeNetworking/comments/1ggnifs/can_anyone_explain_what_does_this_wifi_router_log/

More dialog, maybe less clear explanation, unless you have got some previous UPnP knowledge.