UPDATE:
.kodi/userdata/Database/Addons19.db is the one causing problems.
After further investigation, I came to conclusion that Youtube addon (version 5.1.8 from official repository) is causing issues.
More precisely - if you play any video, and later you restart your raspberry pi, Addons19.db somehow gets corrupt and DLNA stops working for some arbitrary reasons.
So the workaround I have so far is to ssh into Pi, and run: rm .kodi/userdata/Database/Addons19.db and then reboot the Pi.
Anyone experiencing the same thing? Can anyone come with a better workaround, or does someone know how to fix this?