Hello ,
This seems like the LACP flapped which made the corresponding interface down in the perticular node which caused the Interface monitoring down and thereby failover of the RG group .
Now we need to investigate more on why the LACP flapped , if we failed to receive an LACP PDU's from connected device of was there any Physical link flap .
For the RCA I hope we need to investigate by checking the logs from the devices .
If the LACP interfaces are down , please check if the LACP keepalives are been exchanged properly between the connected devices .
Try re-starting the LACP services to see if that helps .