Just wanted to post a followup. Theres been no response from support. I have since reverted back to using Router Mode only as performance is as expected in this setup. But for anyone looking to use...

@David-TP After an initial email I have not heard anything back about the issue.

@David-TP Hi, I checked but I don't see any email yet. Thanks

@David-TP Here is a test from the 2nd deco. https://www.speedtest.net/my-result/a/8824870283 Before when it was in router mode both would have similar results to the above. Here is a result with the...

@David-TP The signal source is ethernet. Here is a speedtest result as well. www.speedtest.net/result/a/8824098968.png

@David-TP It is reproducable 100% of the time. Due to the location of the 2nd deco I can't directly connect them with a single cable. It goes router > switch and then to deco 1. That 1st switch is...