Issue –

The target database, ‘xxx’, is participating in an availability group and is currently not accessible for queries. Either data movement is suspended or the availability replica is not enabled for read access. To allow read-only access to this and other databases in the availability group, enable read access to one or more secondary availability replicas in the group.  For more information, see the ALTER AVAILABILITY GROUP statement in SQL Server Books Online. (Source: MSSQL_REPL, Error number: MSSQL_REPL20015)

Cause – This issue occurs when database is participating in Always-On as well as Replication and Primary Server is your publisher server and when you perform the fail over from publisher server databases on Publisher servers are not accessible hence replication job not able to access those databases and it start failing with above error message.

Resolution –  Check replication role and verify publisher is playing Primary Role in HA. if Not perform the fail-over. After fail-over ensure database is accessible

USE Distribution 
GO 
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED 
-- Get the publication name based on article 
SELECT DISTINCT  
srv.srvname publication_server  
, a.publisher_db 
, p.publication publication_name 
, a.article 
, a.destination_object 
, ss.srvname subscription_server 
, s.subscriber_db 
, da.name AS distribution_agent_job_name 
FROM MSArticles a  
JOIN MSpublications p ON a.publication_id = p.publication_id 
JOIN MSsubscriptions s ON p.publication_id = s.publication_id 
JOIN master..sysservers ss ON s.subscriber_id = ss.srvid 
JOIN master..sysservers srv ON srv.srvid = p.publisher_id 
JOIN MSdistribution_agents da ON da.publisher_id = p.publisher_id  
     AND da.subscriber_id = s.subscriber_id 
ORDER BY 1,2,3