Reply by brtech

While I suspect you are right that the problem is the step down to 2 1/2, a better solution would be 4” all the way, rather than 2 1/2” all the way. He has the Griz with the canister, which has enough oomph for the 4”.

Of course. 17’ of flex is pretty bad.

Consider replumbing with 4” PVC, or PVC to within a couple of feet and then 4” flex to the planer.
If you do that: no 90s, only 45s and a short section of straight duct.

And the Thein separator is a really good idea.