Inbound call to ringgroup knocks user out of checking voicemail

FreePBX distro 5.211.65-1
Asterisk 11.8.1
Digium D40 & D70 phones

Inbound calls ring to a ringroup. If a member of the ringroup is checking their voicemail via the Digium phone visual voicemail app on the Digium D70 and a new call comes in, it knocks them out of the voicemail app on the phone.

It’s as if the FreePBX system does not see the line as busy. Has anyone else seen this behavior?