Availability Groups Service Account has over 25000 sessions open
This is most likely because you have enabled the Log to table option in the agent job step. 

Run 

SELECT spid, 
       program_name,  
       db_name(dbid) AS databasename
FROM   sys.sysprocesses 
WHERE  spid &gt; 50 


or if you have sp_whoisactive installed (http://whoisactive.com/)

EXEC sp_whoisactive 
     @output_column_list = '[%dd%][session_id][sql_text][%database%][login_name][program_name]' /* if they are sleeping spids, add @show_sleeping_spids = 2*/


Get the uniqueidentifier of the job from the program_name, then run

SELECT name
FROM   msdb.dbo.sysjobs 
WHERE  CONVERT(BINARY(16), job_id)=0x[id]


Replace 0x[id] with your id. Once you get the job name, go to the job step, then un-check the log to table option.