Primarily affected VRRP (approx. every 2 hours). UDLD affected once a day around the same time.
VRRP master stops sending VRRP advertisements (no packet captured by optical tap and no advertisement sent as per the debugging logs) which forces the backup member to become master for anywhere between 20-90 seconds with majority of cases lasting around 50s. After this period, all of the missed advertisements are sent in burst and continues to send them (from original master). The former backup member assumes its former role.
CDP packets are being sent and received during the interval as well as any data traffic in both directions.
As a result, the VRRP backup member logs state transition but the dedicated VRRP master has no knowledge of any transition occurring. Which also results in asymmetric data forwarding, since the backup member sent gratuitous ARP after transitioning to master, but no such action was taken by the original Master.