DATABASE lacks a quorum of nodes for high availability

Just after setting up successfully alwayson - availability group, testing the failover, I get this error message: TITLE: Microsoft SQL Server Management Studio ------------------------------ Failed to resume data movement in database 'APCORE', which resides on the availability replica 'MY_SERVER' in the availability group 'AG_TS'. (Microsoft.SqlServer.Smo) For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=14.0.17289.0+((SSMS_Rel_17_4).181117-0805)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&LinkId=20476 ------------------------------ ADDITIONAL INFORMATION: An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo) ------------------------------ Unable to access database 'APCORE' because it lacks a quorum of nodes for high availability. Try the operation again later. (Microsoft SQL Server, Error: 988) For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&ProdVer=14.00.1000&EvtSrc=MSSQLServer&EvtID=988&LinkId=20476 ------------------------------ BUTTONS: OK ------------------------------ what I have is a Quorum for 3 nodes AlwaysOn Availability Group my windows server 2016 cluster has a quorum disk set up: There is a related question here: Failover Cluster Instance work without quorum What does that message mean?