Internet connection required for playing Denon HEOS playlist (with local music)?

My ISP recently had an outage, so no internet. I am trying to keep as many things/automations working in such a case. I noticed that my Denon Heos speaker, that I use as an alarm clock radio, did not start playing in the morning. HA is supposed to start a playlist (created in the Heos app earlier), which consists of local music via DLNA (Plex). Normally this works fine.

Is this to be expected? In that case I am wondering if the classification ‘local push’ in the HEOS documentation is correct. https://www.home-assistant.io/integrations/heos/