When OSPF is also enabled on the VRRP routers
When OSPF is enabled on the routers and a fail-back event occurs, the owner router immediately takes control of the VIP and provides the default gateway functionality. If OSPF has not converged, the route table in the owner router may not be completely populated. When the hosts send packets to the default gateway, the owner router may not know where to send them and packets may be dropped.
CAUTION:
While you can run OSPF and VRRP concurrently on a router, it is best not to run VRRP with other routing protocols, such as RIP or OSPF, on the same interface or VLAN, as this can create operational issues.