The Sleep Number bed somehow is sending an invalid domain to the DNS server (at least it seems that way). Find the queries it sends in the dnsmasq log (/var/log/pihole.log) and share what you find.
Oct 11 07:07:02 dnsmasq[13446]: 157 192.168.0.214/51327 query[A] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:07:02 dnsmasq[13446]: 157 192.168.0.214/51327 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.220.220
Oct 11 07:07:02 dnsmasq[13446]: 158 192.168.0.214/51327 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:07:02 dnsmasq[13446]: 158 192.168.0.214/51327 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.220.220
Oct 11 07:07:02 dnsmasq[13446]: 157 192.168.0.214/51327 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:07:02 dnsmasq[13446]: 158 192.168.0.214/51327 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:07:02 dnsmasq[13446]: 159 192.168.0.214/42348 query[A] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:07:02 dnsmasq[13446]: 159 192.168.0.214/42348 forwarded https://prod-dg.sleepiq.sleepnumber.com.MyHouse to 192.168.0.1
Oct 11 07:07:02 dnsmasq[13446]: 160 192.168.0.214/42348 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:07:02 dnsmasq[13446]: 160 192.168.0.214/42348 forwarded https://prod-dg.sleepiq.sleepnumber.com.MyHouse to 192.168.0.1
Oct 11 07:07:02 dnsmasq[13446]: 159 192.168.0.214/42348 reply https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:07:02 dnsmasq[13446]: 160 192.168.0.214/42348 reply https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:07:02 dnsmasq[13446]: 161 192.168.0.214/50947 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Oct 11 07:07:02 dnsmasq[13446]: 162 192.168.0.214/50947 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Oct 11 07:22:02 dnsmasq[13731]: 496 192.168.0.214/40126 query[A] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:22:02 dnsmasq[13731]: 496 192.168.0.214/40126 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.220.220
Oct 11 07:22:02 dnsmasq[13731]: 497 192.168.0.214/40126 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:22:02 dnsmasq[13731]: 497 192.168.0.214/40126 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.220.220
Oct 11 07:22:02 dnsmasq[13731]: 496 192.168.0.214/40126 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:22:02 dnsmasq[13731]: 497 192.168.0.214/40126 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:22:02 dnsmasq[13731]: 498 192.168.0.214/50073 query[A] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:22:02 dnsmasq[13731]: 498 192.168.0.214/50073 forwarded https://prod-dg.sleepiq.sleepnumber.com.MyHouse to 192.168.0.1
Oct 11 07:22:02 dnsmasq[13731]: 499 192.168.0.214/50073 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:22:02 dnsmasq[13731]: 499 192.168.0.214/50073 forwarded https://prod-dg.sleepiq.sleepnumber.com.MyHouse to 192.168.0.1
Oct 11 07:22:02 dnsmasq[13731]: 498 192.168.0.214/50073 reply https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:22:02 dnsmasq[13731]: 499 192.168.0.214/50073 reply https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:22:02 dnsmasq[13731]: 500 192.168.0.214/56121 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Oct 11 07:22:02 dnsmasq[13731]: 501 192.168.0.214/56121 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Oct 11 07:37:02 dnsmasq[13731]: 1286 192.168.0.214/56801 query[A] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:37:02 dnsmasq[13731]: 1286 192.168.0.214/56801 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.222.222
Oct 11 07:37:02 dnsmasq[13731]: 1287 192.168.0.214/56801 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com from 192.168.0.214
Oct 11 07:37:02 dnsmasq[13731]: 1287 192.168.0.214/56801 forwarded https://prod-dg.sleepiq.sleepnumber.com to 208.67.222.222
Oct 11 07:37:02 dnsmasq[13731]: 1286 192.168.0.214/56801 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:37:02 dnsmasq[13731]: 1287 192.168.0.214/56801 reply https://prod-dg.sleepiq.sleepnumber.com is NXDOMAIN
Oct 11 07:37:02 dnsmasq[13731]: 1288 192.168.0.214/51297 query[A] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:37:02 dnsmasq[13731]: 1288 192.168.0.214/51297 cached https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:37:02 dnsmasq[13731]: 1289 192.168.0.214/51297 query[AAAA] https://prod-dg.sleepiq.sleepnumber.com.MyHouse from 192.168.0.214
Oct 11 07:37:02 dnsmasq[13731]: 1289 192.168.0.214/51297 cached https://prod-dg.sleepiq.sleepnumber.com.MyHouse is NXDOMAIN
Oct 11 07:37:02 dnsmasq[13731]: 1290 192.168.0.214/52595 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Oct 11 07:37:02 dnsmasq[13731]: 1291 192.168.0.214/52595 reply prod-dg-legacy.sleepiq.sleepnumber.com is <CNAME>
Pi-hole is acting correctly in this case. It received a query from a client, forwarded it up, and since it was a bad request, the upstream sent an NXDOMAIN response, which Pi-hole returned to the client. You can try manually entering the URL into this /etc/pihole/setupVars.conf setting:
A further option if you want to never see this client in your Pi-Hole and you are using the DHCP server in your Pi-Hole - exclude that client from Pi-Hole and give that client a third party DNS address.
I do have a separate VLAN for my "No-Pihole" clients but, it's currently restricted to wired clients only. I didn't wan't to set up a separate SSID for this one wireless client just to give a different DNS via DHCP for this one nuisance client.. I even consider how I might manually assign DNS to the bed but, there isn't exactly a customer facing user interface for that.