(more specifically public lan was unreachable unless hard reset) and only replication lan was working giving us this issue:
1. Host server with problems was reachable via RDP from working host using Replication lan ip/subnet.
2. Cluster was ok but VM that was backing up mode was locked.
3. We was not able to live migrate vm from one host to another or any other action. (shutdown, hard reset....)
Here they are action taken to solve issue other then temporary HyperV freezes hard reset.
Veeam B&R showed that there was missing on both hosts these Microsoft hotfixes (please be aware to take note about patch prerequisites before installation)
Host: XXXXXXX
KB3068444: Resolves an issue where a cluster node experiences a Stop 0xF5 FLTMGR_FILE_SYSTEM when using Shared VHDX. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
Description: Resolves an issue where a cluster node experiences a Stop 0xF5 FLTMGR_FILE_SYSTEM when using Shared VHDX. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
https://support.microsoft.com/en-us/kb/3068444
KB3068445: Resolves an issue where a deadlock or Stop 0x9E occurs on a cluster node when there is a lot of network (SMB) I/O requests to large files (1 TB or more). Includes the fix from 3044457. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
Description: Resolves an issue where a deadlock or Stop 0x9E occurs on a cluster node when there is a lot of network (SMB) I/O requests to large files (1 TB or more). Includes the fix from 3044457. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
https://support.microsoft.com/en-us/kb/3068445
KB3072380: Resolves an issue on a Hyper-V cluster where the heartbeat component times out during a long-running snapshot. The snapshot fails and the VM restarts. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
Description: Resolves an issue on a Hyper-V cluster where the heartbeat component times out during a long-running snapshot. The snapshot fails and the VM restarts. Available for individual download. To apply this update, you must first install the update 2919355 on Windows Server 2012 R2.
https://support.microsoft.com/en-us/kb/3072380
KB3090343: Cluster service stops during the VSS backup in a Windows Server 2012 R2-based Hyper-V cluster.
Description: Resolves an issue an issue that occurs when you use the Volume Shadow Copy Service (VSS) backup on a Cluster Shared Volumes (CSV) volume by using a software snapshot provider in Windows Server 2012 R2.
https://support.microsoft.com/en-us/kb/3090343
Meanwhile we verified Firewall status and we verified that Following AV exclusions was working fine.
*.AVHD
*.AVHDX
*.ISO
*.VHD
*.VHDX
C:\ClusterStorage\Volume1\
C:\ProgramData\Microsoft\Windows\Hyper-V\
Vmms.exe
Vmwp.exe
After these actions problem was successfully solved.
Here there is another veeam article (that successfully apply to veeam 9.0 too after veeam support querying)
