It looks like Viber is putting a halt on the further development of their Windows 10 UWP apps until further notice. In an email sent to one of their customer, the company noted that due to the lack of resources, development of Windows 10 apps has been put to a halt until further notice. Below are the tidbits from the email.
In order to allocate our limited company resources in the most efficient way possible, we have decided to put any updates for Windows Phone 10 and Windows 10 on hold until further notice.
There are no version releases planned in the forseeable future. We will address this issue if our plans change and a decision is made to release an update.
We apologize for the inconvenience.
The email, however, leaves some room for speculation and with regular updates in the past, it will take time before the app gets fully abandoned. For now, the app looks to work perfectly well with no issues whatsoever.
You can download the current Viber app from the Windows Store Here.