@KingR 

This may not be the answer you are looking for, but its honest and from nearly 20 years working with WiFi..   You dont have an issue here

WiFi will always experience packet loss, its expected that some of the tx / rx packets will be corrupted upon arrival and need to be retried before forwarding (LAN or WiFi) resulting in loss being incurred.  In normality anything below 5% is perfect, 10% is considered good, it only starts becoming an issue when you get to 30% loss.

The fact you get no loss when connected to LAN only indicates its the WiFi packets being retried which comes as no surprise.  Honestly, wouldnt waste your time chasing this as it aint going to disappear!

My current connection for example is experiencing 6% packet loss, more than likely as the family are hammering netflix and whatever in the background :)  However its causing ZERO issues and thats on a much more expensive business grade network, on a deco 3% I would take any day as perfect.

  @Philbert I appreciate your response. However dispute you assertion that 10% should be seen as good. That's pretty terrible and would destroy anything real time like gaming or video. 
 

Just for info, this was a device literally next to the mesh node and no other activity at the time. Maybe I should consider myself lucky because this is the first time I've seen levels of packet drops with any other brand or setup, but then this is the first time I've got a mesh network. It's impacting my ability to work so I need to fix it one way or another!

  @KingR 

The distance from a mesh node is pretty irrelevant to packet loss, if anything the higher transmit power over the shorter distance can be negative factor.  When doing surveys for WiFi one must consider that too close is also an issue.

Any dropped / lost packets will be retransmitted in the majority of cases and isn't an issue in UDP traffic where loss is a given, that aside, if you are averaging 2-3% then thats perfectly in expectations IMHO and with a Mesh setup one would expect that, if not higher.

Below is a controller for 12 APs, they average around 3% loss overall, odd spike to 10% during peak sessions but overall its well below the margins that the controller indicates as an issue..  personally i think 40% is way too high myself, but both Omada and Ubiquiti dont alert at anything below 10%

However if you feel that your current 3% is too high for you, then by all means there are plenty of ways to reduce this, just have a google.   However my opinion, in a mesh setup its well within specifications.

  @Philbert 

I have the exact issue with my XE75 tried reaching out to support but they were no help