I don’t have any issues with them on wifi. The Heos units don’t use Airplay, the iOS devices are just using apps to control them but the music streams direct from wifi.
I have a couple of Denon HEOS speakers and have the same issue trying to stream to them via Bluetooth from either my iPhone or iPad. Streaming from other devices via Bluetooth works fine without the stutter like the iOS devices do. I did a deep Google search a while back and there are other...