Hello Trevulate! Thank you for participating in the Apple Support Communities.
We understand that Siri isn't playing request songs on HomePod, but you're able to play those same songs on another device and AirPlay to HomePod. We'd like to look into this with you to see how we can help.
Does restarting your HomePod have any effect on this issue? This can be done with the following steps: Open the Home app on your iPhone, iPad, iPod touch, or Mac. On iPhone, iPad, or iPod touch, press and hold HomePod. On Mac, double-click HomePod. Scroll down and tap or click Reset HomePod, then select Restart HomePod.
If the issue persists, let's restart the modem and router for your network.
Make it a great day!