Cause 1:
1. Expand the SQL Server SSMS
2. select the SQLAGENT
3. Right click and select properties
4.Check the properties in the connection TAB at SQL Server.
Check if SQL Server alias is pointing to different server. If yes change it back to default and restart SQL Server

Cause 2:
In correct MSX/TSX configuration or MSX/TSX

Cleaned up system tables related to MSX-TSX in MSDB and reconfigure MSX/TSX configuration and jobs.
systargetservergroupmembers
systargetservergroups
systargetservers
You can run ‘sp_msx_enlist’ at target server and check the output error if there has some error happened.

Cause 3:
Disable encryption.certificate validation are enabled for connections between master servers and target servers by default.
   a) “Start”->”run”->type “regedit” at ‘GSHJRQA’ server.
   b) Navigate to \HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\\SQLServerAgent\MsxEncryptChannelOptions(REG_DWORD)
   c) Change “MsxEncryptChannelOptions” value from 2 to 0.