Voice Control files randomly keep having to re-download

Voice Control on this iPad 10th gen is kept on continuously, and the device is always plugged in to power. The "go to sleep" VC command is used when the device is not in use. But almost daily, VC will stop functioning altogether and need to be toggled off/on. However upon toggling back on, it will then start re-downloading the VC vocabulary files which is a time consuming process.

It is very troubling for the device user, who is quadriplegic.

Can anybody shed some light why this could be happening?