Poly VVX Hookswitch Mode setting reverts after the reboot which happens when a setting is saved (Settings, Basic, Preferences, Headset).
- Poly VVX 300, 301, 400, 410
- Poly Firmware (version 5.9.1.0615)
Note: Possibly affects other Poly VVX devices also.
As a workaround, the firmware can be downgraded by 8x8 to an earlier version that is not affected.