Cannot send media in Viber

I'm in an organization where we have Application Control enabled in our FortiGate. We have allowed Viber within the Application Control, but for some reason, we can send messages except for media files. This seems to be inconsistent too as some members of the organization can send despite being in the same IP address range.

Viber has been allowed in the Application Control since I got in the organization, but this problem suddenly occurred last week. How can this be solved?

EDIT: I can confirm that this is not a Viber problem because if we disable the Application Control, we can send media, but disabling Application Control is not an ideal solution for our organization.