RT-AX86U – AiProtection + QNAP HybridSync Mount Failures After Updating to 3004.388.10 (Resolved by Downgrade to 388.9)

[themilfalcon]

Hi all,


Posting this in case others run into the same issue, and to understand if there’s a known cause.


Router: RT-AX86U (Zaku II Edition)
Previous stable: 3004.388.9 (Merlin)
Updated to: 3004.388.10 (Merlin)
NAS Setup: Two QNAP units (latest QTS), syncing daily using Hybrid Backup Sync (mount-based file replication, not rsync push)

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Issue After Updating to 3004.388.10​

Immediately after upgrading to 3004.388.10, my scheduled QNAP → QNAP HybridSync jobs started failing intermittently:

• Remote NAS hostname resolved normally
• Mounts would either fail outright, or mount but stall partway through file operations
• Manual sync attempts from QNAP UI also failed

No network, DNS, or NAS configuration changes were made — the only change was the router firmware update.

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Additional Finding:​

Although the web UI showed AiProtection enabled, the Trend Micro DPI components were not running:

• DPI processes were absent in ps
• No intrusion/web filter logs were appearing
• Restarting the firewall or toggling AiProtection did not start DPI services

This suggests that DPI / firewall module load order or initialization may have been affected in 3004.388.10.


Since QNAP mount and file sync flows pass through the DPI chain, this could explain the mount instability and stalled sync transfers.
Tried a hard reset and also tried a reset by clearing the NVRAM. The problem did not go away.

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Resolution​

I downgraded back to 3004.388.9:

• AiProtection / DPI processes immediately resumed normal operation
• QNAP HybridSync mounts and transfers now run fully stable, as before

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Request to Community / Developers​

• Has anyone else seen AiProtection not actually running under 3004.388.10?
• Is there a known change to DPI, netfilter hooks, or service startup order in this release?
• If needed, I can capture logs before/after.

Posting this in case it helps others diagnosing similar symptoms.


Thanks to everyone contributing to Merlin — it has been rock solid for my environment outside of this one case.

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[ColinTaylor]

Can you clarify:

This is a backup (or sync) between two QNAP servers. Are these servers on the same LAN, or are they in different locations and you're doing this over the internet?

As this is a Merlin sub-forum can you briefly explain what underlying protocol this "HybridSync" uses. You said it isn't rsync.

 

[themilfalcon]

1. Network Topology


Both QNAP units are on the same LAN, same subnet:

QNAP #1 → RT-AX86U → QNAP #2

No VPN, no WAN routing involved.
This is strictly LAN-side, internal traffic.

2. Hybrid Backup Sync Protocol Used
Hybrid Backup Sync (HBS3) supports multiple transfer modes (rsync, RTRR, S3, etc).


However, in this case, the job is configured as a mount-based sync, meaning:

• QNAP #1 mounts a shared folder on QNAP #2 directly using SMB (CIFS)
• Then performs a local file-level comparison + copy, not rsync push.

To emphasize:
This is not rsync and not RTRR over WAN.
It’s SMB over LAN, initiated by one QNAP mounting the other like a local network share.

Thanks

 

[ColinTaylor]

Thanks for the info.

Given this is LAN to LAN traffic I can't think why the router's firmware would have any bearing. The only time the NAS traffic hits the router is when it's switched between the LAN ports (assuming both are ethernet connected). None of the traffic is being routed so things like AiProtection, DPI, firewall, QoS, etc. don't come into play.

Does the NAS have any logging that might give a clue?

I suppose it's possible that the router was having major problems more generally (e.g. reboot loop, processes crashing or CPU at 100%), and that the NAS issues were just a side effect of that. Any clues in the router's System Log - General Log?

 

[bennor]

@themilfalcon, as ColinTaylor suggested, check the logs on both the router and both NAS's to see what information they might shed as to what's happening around the time the NAS's are performing a backup.

What other troubleshooting steps have you tried?
Have you tried restarting the router and both NAS's?
May have missed it, but are you running any addon scripts on the router or have any custom configurations added via SSH to the router?
Disable the router's AiProtection AND withdraw from it on the Administration > Privacy (or Policy) page as a troubleshooting step.
Does the NAS to NAS backup fail randomly or at a specific location/time in the backup?

Also, if possible can you clean up your posts a bit to remove the extra blank lines? It makes the post(s), particularly your first post, flow like a wall-o-text with multiple blank lines between sentences, paragraphs, and bulleted list blocks.