Every time I try to use voice control on my Homepods, I get "Sorry the operation couldn't be completed. HMErrorDomain error 3"

This has only started happening within the last few weeks. Prior to this, my voice worked perfectly on both of my homepods, and on Siri across all my Apple devices. Now whenever I try to control something with my voice (turn lights on or off, change the AC etc), I get "Sorry <MY NAME>, something went wrong. The operation couldn't be completed. HMErrorDomain error 3". However, using the Home app to manually switch the lights on or off works perfectly every time.

This error message doesn't tell me anything meaningful.

My Homepods are all up to date (checked in Home > Home Settings > Software Update) and my iPhone 15 PM and iPad Pro are definitely up to date. No devices are on any betas.

Can anyone assist please?