ACP 15.0.26172 and ESXi 6.7 configuration backup - Failed to connect to ESXi host by using SSH

I have two ESXi 6.7 hosts under my vCenter, both protected by ACP 15.0.26172.
Host 1: VMware ESXi, 6.7.0, 16316930
Host 2: VMware ESXi, 6.7.0, 17167734
When trying to backup the ESXi configuration, the backup of Host 1 is OK. No issues.
However, when trying the same on Host 2 (slightly newer ESXi build) I get this:
MESSAGE
Failed to connect to ESXi host 'xxx.xxx.xxx.xxx' by using SSH.
Additional info:
------------------------
Error code: 20250646
Fields: {"$module":"mms_bundle_glxa64_26172","CommandID":"F30407D6-601F-11E0-9C67-FF46DFD72085"}
Message: TOL: Failed to execute the command. Backup workflow
------------------------
Error code: 20250646
Fields: {"$module":"mms_bundle_glxa64_26172","CommandID":"F30407D6-601F-11E0-9C67-FF46DFD72085"}
Message: TOL: Failed to execute the command. Backup workflow
------------------------
Error code: 21561346
Fields: {"$module":"mms_bundle_glxa64_26172","StepType":2,"TraceLevel":1}
Message: Step 'Backup' has failed.
------------------------
Error code: 20250646
Fields: {"$module":"mms_bundle_glxa64_26172","CommandID":"4504F8D4-2727-42AB-BB4F-A42EDBB790A0"}
Message: TOL: Failed to execute the command. Tol::IsolateCommand
------------------------
Error code: 20250646
Fields: {"$module":"service_process_glxa64_26172","CommandID":"8F01AC13-F59E-4851-9204-DE1FD77E36B4"}
Message: TOL: Failed to execute the command. Backing up
------------------------
Error code: 20250646
Fields: {"$module":"gtob_backup_command_addon_glxa64_26172","CommandID":"8F01AC13-F59E-4851-9204-DE1FD77E36B4"}
Message: TOL: Failed to execute the command. Backing up
------------------------
Error code: 21561347
Fields: {"$module":"disk_bundle_tape_off_glxa64_26172"}
Message: Failed to back up the configuration of ESXi host 'xxx.xxx.xxx.xxx'.
------------------------
Error code: 30015501
Fields: {"$module":"disk_bundle_tape_off_glxa64_26172"}
Message: Failed to back up the configuration of ESXi host 'xxx.xxx.xxx.xxx'.
------------------------
Error code: 30015497
Fields: {"$module":"disk_bundle_tape_off_glxa64_26172"}
Message: Failed to connect to ESXi host 'xxx.xxx.xxx.xxx' by using SSH.
SSH is enabled on both and a test with PuTTY gives no error and I can access the ESXi shell console on both.
There are no other backup issues for any of the VM's on either of these hosts.
Is there an issue with certain ESXi 6.7 builds?
Is it something else?
Neil

Thanks Maria. I'll get on to support.
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Hello Neil.
Otherwise, I advise that you install Agent for VMware (Virtual Appliance) on the second host and see if the issue remains.
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Best regards,
Maria Belinskaya | Acronis Forum Support Specialist
Information provided AS-IS with no warranty of any kind.
To contact support, please follow http://www.acronis.com/en-us/support/

Hi Maria,
The Virtual Appliance's for VMware are already installed on all ESXi hosts. How else would the VM backups work?
I opened a ticket with support. Haven't received any response or even an acknowledgement of the ticket being received.
I'm going to try the online chat to see if that wakes anyone up!
EDIT: Found the support ticket history; you don't make it easy to find :) Chat just threw me back to the support page on my account. :(
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Had this back from Acronis support:
I have checked my internal resources and found that there is known issue with VMware ESXi, 6.7.0, build # 17167734. So, backup will not work at the moment. The fix will be implemented in the upcoming builds. We do not have information when the fix will be released. Once the fix will be released, you will be notified.
So, yes, there is an issue with certain builds of ESXi 6.7.
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Hello Neil,
thank you for sharing the outcome!
I also returned to this forum thread to announce that this is a known issue (ABR-306827) which is going to be fixed in one of the following updates.
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Best regards,
Maria Belinskaya | Acronis Forum Support Specialist
Information provided AS-IS with no warranty of any kind.
To contact support, please follow http://www.acronis.com/en-us/support/

Good to know that I am not the only one affected by this issue.
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Hello Community,
we got the same issue with the VMware Build # 17167734.
Any solution for this problem?
We use:
Richard
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Dear Richard,
as per the records in our internal system, the ticket /ABR-306827 Backup of ESXi 6.7 configuration fails with "Failed to connect to ESXi host by using SSH" is still open and the developers are working on a fix. In the meantime, please open a support ticket , so that our engineers can look at your environment and suggest a workaround till the fix is released.
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Best regards,
Ekaterina Surkova | Forum Moderator
Information provided AS-IS with no warranty of any kind.
To contact support, please follow http://www.acronis.com/en-us/support

This issue seems not to be fixed in update 2, unfortunately.
Best greetings from Germany
Olaf
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Hello Olaf.
Yes, ABR-306827 is still at work.
Our engineers suggest the following as a workaround option:
Please, save /etc/ssh/sshd_config somewhere as a backup file.
Don't place it on the host, especially /etc/*, since unrecognized files can be removed after a reboot. After that, open /etc/ssh/sshd_config on the ESXi host and check whether you have KexAlgorithms field or not. If so, add "diffie-hellman-group14-sha1" at the end of the comma separated list. If you don't have this field, paste the following at the end of the file: "KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1".
This is a list of default key exchange algorithms with diffie-hellman-group14-sha1.
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Best regards,
Maria Belinskaya | Acronis Forum Support Specialist
Information provided AS-IS with no warranty of any kind.
To contact support, please follow http://www.acronis.com/en-us/support/

Thanks this did work (just tested with Update 4).
Best greetings from Germany
Olaf
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Best regards,
Maria Belinskaya | Acronis Forum Support Specialist
Information provided AS-IS with no warranty of any kind.
To contact support, please follow http://www.acronis.com/en-us/support/