DHCP failure: NACK

I set up a local DHCP server at home and disabled the DHCP running on my internet provider modem. My laptop, phone & tablet are working fine and are able to get an IP however I have troubles with my sonos wifi speaker: it keeps sending DHCP requests like this:

enter image description here is the DHCP server. is the modem. I guess the problem is the NACK request sent by the modem (the DHCP server is disabled on it though)... The pcap file is available here: https://ufile.io/vaubc Any idea about what's wrong here?