Avamar GC failing with MSG_ERR_NOTAVAILABLE

Avamar GC kicks off and then rapidly fails with MSG_ERR_NOTAVAILABLE. 

Stale sessions were left from a node replacement/restart.
These stale backup/replication/recovery sessions can cause Avamar GC to fail with MSG_ERR_NOTAVAILABLE.

Note the status.dpn output shows 22 dispatchers (Dis column). 
      ***Note 1-3 dispatchers on an idle system is normal.***
admin@avamar:~/>: status.dpn: 
Node   IP Address   Version                        State      Runlevel   Srvr+Root+User   Dis Suspend Load UsedMB Errlen  %Full   Percent Full and Stripe Status by Disk
0.7   192.168.255.9 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   4 false   0.15 31582 34980635   5.4%   5%(onl:3098)  5%(onl:3076)  5%(onl:2980)
0.6   192.168.255.8 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   0 false   0.12 31583 24206783   5.4%   5%(onl:3055)  5%(onl:3021)  5%(onl:3074)
0.5   192.168.255.7 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   5 false   0.05 31578 32931941   5.4%   5%(onl:3018)  5%(onl:3051)  5%(onl:3059)
0.4   192.168.255.6 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   2 false   0.35 31590 30437344   5.2%   5%(onl:2983)  5%(onl:3033)  5%(onl:3035)
0.3   192.168.255.5 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   0 false   0.18 31574 14831616   5.4%   5%(onl:3102)  5%(onl:2994)  5%(onl:3043)
0.2   192.168.255.4 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   0 false   0.46 31575 13085565   5.2%   5%(onl:3014)  5%(onl:3033)  5%(onl:3024)
0.1   192.168.255.3 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   5 false   0.11 31581 36028694   5.3%   5%(onl:3046)  5%(onl:3055)  5%(onl:2990)
0.0   192.168.255.2 7.5.1-101_HF310405  ONLINE fullaccess mhpu+0hpu+0hpu   6 false   0.04 31585 34078136   5.3%   5%(onl:3029)  5%(onl:3063)  5%(onl:3028)

Confirm there are no active backup or replication sessions with mccli and avmaint commands
admin@avamar:~/>: mccli activity show --active       
0,23000,CLI command completed successfully.
ID Status Error Code Start Time Elapsed End Time Type Progress Bytes New Bytes Client Domain
-- ------ ---------- ---------- ------- -------- ---- -------------- --------- ------ ------
admin@avamar:~/>:

admin@avamar:~/>: avmaint sess | grep path
admin@avamar:~/>:

This particular issue started when a node was rebooted due to ping no ssh situation. 
Multiple dispatchers show on status.dpn output, but there are no corresponding activities are shown by avmaint sess or mccli activity show.
Avamar GC performs a check at startup which the stale sessions interferes with.
Confirm with backup team that its OK to kill all session, stop them via gui or cmd line.
Once all sessions were killed and had died off use the following to recycle maint and restart GC.
dpnctl stop maint
dpnctl start maint

GC should then start a new attempt and process successfully.

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Similar issue with different cause @ 461984 : Avamar - GC fail with MSG_ERR_NOTAVAILABLE https://support.emc.com/kb/461984