In a post on German website WindowsArea.de, Viber has apparently ceased development on its Windows 10 Universal app for Windows 10 and Windows 10 Mobile, at least until further notice.
In an email, a member of the Viber Support Team, Trinity L., stated that "in order to allocate our limited company resources," Viber has ceased future development and no new updates will be available for Viber on Windows 10 or Windows 10 Mobile. The full email is below.
Viber's decision seems like its not a complete abandonment of Windows 10 and Windows 10 Mobile. Viber stated in the email that they will reassess their decision in the future and may release an update "if their plans change."