Using Ubuntu 16.04 with all upgrades. Viber stopped loading after upgrade to latest version 6.5.5. Problem remained after clean reinstall of Ubuntu.
Below is the output of  /opt/viber/Viber
    /opt/viber/Viber
QSqlDatabasePrivate::removeDatabase: connection 'ConfigureDBConnection' is still in use, all queries will cease to work.
Qt WebEngine ICU data not found at /opt/viber/resources. Trying parent directory...
Qt WebEngine resources not found at /opt/viber/resources. Trying parent directory...
Qt WebEngine ICU data not found at /opt/viber/resources. Trying parent directory...
Qt WebEngine resources not found at /opt/viber/resources. Trying parent directory...
QXcbConnection: XCB error: 3 (BadWindow), sequence: 508, resource id: 54525979, major code: 2 (ChangeWindowAttributes), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 509, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 510, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 511, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 513, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 514, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 515, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 519, resource id: 54525979, major code: 18 (ChangeProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 523, resource id: 54525979, major code: 2 (ChangeWindowAttributes), minor code: 0
    ................
Cannot make it work, cannot find previous version that worked.
Help will be highly appreciated!
 
    