What is causing the Avamar Client to scan files slower

One of mu Avamar backup for windows file system encounter a problem, since a week ago,the backup became very slow. i the time for backup this server suddenly  increased almost 6 hours, it used to take less thane 8 hours to finish the backup job, means now it take more than 14 hours to finish the backup jobs for this server.

we have not change anything(CPU,Memory,bandwidth) for this server. i suspect the speed of scaning file become slow which lead to take more time to backup the server. 

Normal Log：

2020-10-05 22:37:15 avtar Info <8650>: Opening filename cache file 'C:\Program Files\avs\var\f_cache2.dat'
2020-10-05 22:37:15 avtar Info <5573>: - Loaded filename cache file (6,532,792 bytes), the value maybe the same as previous backups.
2020-10-05 22:37:15 avtar Info <8650>: Opening hash cache file 'C:\Program Files\avs\var\p_cache.dat'
2020-10-05 22:37:16 avtar Info <5573>: - Loaded hash cache file (805,306,912 bytes), the value maybe the same as previous backups.
2020-10-05 22:37:19 avtar Info <6426>: Done loading cache files2020-10-05 23:57:03 avtar Info <40069>: Backup /cur/07bdec948cf16154e5e199979c40e88f4fa3943f/1D69B302B189C0E has 1 file on the Data Domain server
2020-10-05 23:57:03 avtar Info <17965>: Final location on DDR 'avamar-1572849800/cur/07bdec948cf16154e5e199979c40e88f4fa3943f/1D69B302B189C0E'
2020-10-05 23:57:04 avtar Info <5375>: 1 match for exclude pattern "\System Volume Information\MountPointManagerRemoteDatabase".
2020-10-05 23:57:04 avtar Info <5375>: 1 match for exclude pattern "outlook.ost".
2020-10-05 23:57:04 avtar Info <5156>: Backup #2838 timestamp 2020-10-05 23:57:03, 3,281,564 files, 261,459 folders, 2,060 GB (1,245 files, 926.8 MB, 0.04% new)
2020-10-05 23:57:04 avtar Info <7539>: Label "Sch_10.30PM-7H-FileSrv10_D-E-1601908200017", scheduled to expire after 11/04/20 (2020-11-04 14:30:00 UTC), daily backup
2020-10-05 23:57:04 avtar Info <6083>: Backed-up 2,060 GB in 79.88 minutes: 1,547 GB/hour (2,464,727 files/hour)
2020-10-05 23:57:04 avtar Info <5587>: Updating cache files in C:\Program Files\avs\var
2020-10-05 23:57:04 avtar Info <5069>: - Writing cache file "C:\Program Files\avs\var\f_cache2.dat"
2020-10-05 23:57:04 avtar Info <18895>: Cache update complete C:\Program Files\avs\var\f_cache2.dat (561 pages in all backups in cache)
2020-10-05 23:57:04 avtar Info <5069>: - Writing cache file "C:\Program Files\avs\var\p_cache.dat"
2020-10-05 23:57:06 avtar Info <5546>: Cache update complete C:\Program Files\avs\var\p_cache.dat (768.0 MiB of 1535 MiB max)
2020-10-05 23:57:13 avtar Info <7883>: Finished at 2020-10-05 23:57:13 China Standard Time, Elapsed time: 0001h:20m:02s
2020-10-05 23:57:13 avtar Info <40176>: - Multi-stream restore summary (current 0, max active 0, max cloned 0, total cloned 0, ddr handle 1):
2020-10-05 23:57:13 avtar Info <8468>: Sending wrapup message to parent
2020-10-05 23:57:13 avtar Info <5314>: Command completed (exit code 0: success)
2020-10-05 23:57:13 avtar Warning <5887>: Possible Windows Domain Controller issue: Windows Security ID lookups: Good: 847 in 0.64 secs = 0.8ms avg, Bad: 131 in 0.09 = 0.7ms avg

when having issue:

2020-10-07 02:34:54 avtar Info <40069>: Backup /cur/07bdec948cf16154e5e199979c40e88f4fa3943f/1D69C0F6293FFFE has 1 file on the Data Domain server
2020-10-07 02:34:54 avtar Info <17965>: Final location on DDR 'avamar-1572849800/cur/07bdec948cf16154e5e199979c40e88f4fa3943f/1D69C0F6293FFFE'
2020-10-07 02:34:54 avtar Info <5375>: 1 match for exclude pattern "\System Volume Information\MountPointManagerRemoteDatabase".
2020-10-07 02:34:54 avtar Info <5375>: 1 match for exclude pattern "outlook.ost".
2020-10-07 02:34:54 avtar Info <5156>: Backup #2846 timestamp 2020-10-07 02:34:54, 3,281,752 files, 261,490 folders, 2,060 GB (552 files, 457.7 MB, 0.02% new)
2020-10-07 02:34:54 avtar Info <7539>: Label "Sch_10.30PM-7H-FileSrv10_D-E-1601994600013", scheduled to expire after 11/05/20 (2020-11-05 14:30:00 UTC), daily backup
2020-10-07 02:34:54 avtar Info <6083>: Backed-up 2,060 GB in 173.31 minutes: 713 GB/hour (1,136,132 files/hour)
2020-10-07 02:34:54 avtar Info <5587>: Updating cache files in C:\Program Files\avs\var
2020-10-07 02:34:54 avtar Info <5069>: - Writing cache file "C:\Program Files\avs\var\f_cache2.dat"
2020-10-07 02:34:54 avtar Info <18895>: Cache update complete C:\Program Files\avs\var\f_cache2.dat (561 pages in all backups in cache)
2020-10-07 02:34:54 avtar Info <5069>: - Writing cache file "C:\Program Files\avs\var\p_cache.dat"
2020-10-07 02:35:01 avtar Info <5546>: Cache update complete C:\Program Files\avs\var\p_cache.dat (768.0 MiB of 1535 MiB max)
2020-10-07 02:35:12 avtar Info <7883>: Finished at 2020-10-07 02:35:12 China Standard Time, Elapsed time: 0002h:53m:36s
2020-10-07 02:35:12 avtar Info <40176>: - Multi-stream restore summary (current 0, max active 0, max cloned 0, total cloned 0, ddr handle 1):
2020-10-07 02:35:12 avtar Info <8468>: Sending wrapup message to parent
2020-10-07 02:35:12 avtar Info <5314>: Command completed (exit code 0: success)
2020-10-07 02:35:12 avtar Warning <5887>: Possible Windows Domain Controller issue: Windows Security ID lookups: Good: 847 in 1.22 secs = 1.4ms avg, Bad: 131 in 0.17 = 1.3ms avg