Contact Center- Queue Voicemail Inbox

[Erin_KPA]

We have a queue inbox for call overflow that has 2 users assigned, and they have reported that sometimes they get the email notification about the voicemail but it doesn't appear in the Contact Center inbox for them, even after refreshing. 
Has anyone else run into similar issues? When I did a test call/VM it behaved as expected, and it only seems to happen sporadically, so I'm not sure what more I can do to address this for the users.