My friend have on his 1.8T car KO4 from RS6, 440 cc injectors, turbular manifold,3 inch straight pipe,FMIC, FORGE DV...
After some remaps and runs, car was running great, except it didn't have enoguht fuel for BTS enrinchment. So we decidet to change fuel filter (car have returnless sitem)
After changing fuel filter, we take run( i didn't log it) car was started to build boost then 'droped' for a half second and again accelerating normaly
Since then, that turbo become so lagy that I can't bellive. It need about 4-5 second to build boost
This was before in 3 gear (full boost slightly before 3000 rpm)

And run after fuel filter change (full boost at 4000 rpm)

When I discconect hose from WG it behavier the same.

I am out of idea what can cause this 
Strange thing after the trubo build boost the car is behavior exactly as before, same boost ,same power same WGDC.  Except now it has enought fuel for BTS
Only difference is in that now build boost a really slow. Do anybody have idea what caused this?

good thing you posted a log.

haven't looked at your logs yet but the most common problem is collapsed inlet or leaking dv.

or blown turbo

These are log maybe bether for compare

https://easyupload.io/qdhbkc

You can see, even with 85% DC it spools slower than before at 80%. Now when I set it to 95% or completly discconect hose from WG it doesen't make significant difference

Yes I thout it might be a turbo, but if turbo is death it doesen't make sense when it behavier same as before once it gets boost

Only difference is that with old filter AFR will go to lean during spool, but I don't think that have so much influence
I already checked air filter, exhaust is straight pipe without CAT... 
My doubt go to DV, I will do one run without it
I don't have tool do boost leak
When you say intake restriction, what it can be?

Very easy to make a tool , just use some pvc pipe and a bike valve and a bike pump with a pressure gauge attached really, but indeed that is strange if you only changed fuel filter.

I can't find any error on engine.
I put stronger spring in DV, tension on WG is good, no colapsing inlet hoses during full throotle, i tried to play with igniton angle and AFR, but it barely made a difference

Tryed that too, same thing. Tried differnet injectors, changed WBO, changed spak plugs
Always same