Hi there, no mention has been made of this Rc Firmware - would be happy to try it if you have a download link?

Okay, apparently the technician was looking to try a different protocol as a troubleshooting step.
You should receive the newer firmware shortly and you can see if that improves the issue. Beyond that, I wonder if it could be a LAN/WAN interoperability issue with switches and whether the packet loss occurs on the LAN/WAN when it occurs on the IPsec VPN, which seems like it does from your previous posts. The firmware update might help with that.

Thanks, it’s happening at two different sites that I have tried and both have LAN switches from different manufacturers but thanks I will try the updated firmware next week and report back.

A further update for anyone following this topic. Draytek support gave me the Release Candidate firmware (4.2.2 RC3) to try but before doing so I connected a PC directly to the 2927 (still on its 4.2.0.1 firmware) and ran a ping test on it's internal IP address. I also experienced occasional packet loss doing this so I wonder if the VPN packet loss is a slight red herring, and packet loss is in fact apparent on the device as a whole.

I then put the 4.2.2 RC3 firmware on it and experienced zero packet loss to the internal IP address so took back out to one of the test sites for further testing.

It was much more stable at the test site using the 4.2.2 RC3 firmware, and I only suffered 3 or 4 dropped packets after around 20 minutes of ping testing to various endpoints (VPN/Internal/Direct to Internet). The packet loss I did experience only occurred over the VPN tunnels (not to the internal LAN address or directly to the Internet). The packet loss did occur in both directions across the tunnel.

However, I noticed on Monday that Draytek.com had released a new official firmware for the 2927 (4.2.0.2) so decided to give that a try. With this firmware I experienced zero packet loss at all after around 30 minutes of continuous ping testing. I decided the leave the 2927 in-situ at the test site, running proper traffic and so far so good (the very first time I took this 2927 out to site the entire office became unstable after around 30 minutes due to the amount of packet loss - unable to use their VoIP phones properly or run our SQL-based practice software without constant link errors - all appears OK at the moment after the few hours it's been running).

Interestingly, the only fix/improvement listed on the release notes for the 4.2.0.2 firmware is "Improved: Optimize the WAN1 interface for compatibility."

I have left the old 2926 in place as a hot-swap backup just in case and am continually monitoring (and will do so for the rest of the week) but hopeful the packet loss issue is resolved with this new official release 4.2.0.2 firmware.

Will report back with further updates early next week.

The office at the other end of this 2927 hasn't reported any issues since I set it up, and while a few of the connected tunnels have lost the odd packet here and there during my testing, the reliability seems much improved.

I've reported back to Draytek support the above, and they have suggested that we may see further improvements in future firmware updates which is hopeful.

We're going to slowly roll these out to our other offices so will report back here with any other findings/info we may think relevant.