MWI on T20P won't turn off after checking messages

[Bobcat19]

So on one of our t20p's, the message waiting indicator light is set to check the voicemails, which is does. However even after deleting them the light stays on.

I have "subscribe to MWI" and "Subscribe MWI to voicemail" both set to enabled, and the subscription period left as default.

Can someone please help me set it up so that it works correctly? Also it probably doesn't help that I don't understand fully what those 3 settings do exactly, so if anyone wants to fill me in, great.

[James_Yealink]

Hi,

The MWI indicator will only light when server send a NOTIFY message with unread voice mail.
Please start a pcap trace then re-register the account, you can see detail info of voice message summary in the NOTIFY packet. Or send it to us.

May I know is the T20 in a ring group or some other group?

Regards,
James