hmmm … well, it could occur at 32 mph b/c at speeds lower than that, the engine needs less fuel flow to run, and the obstruction isn’t blocking the fuel flow enough to prevent enough gas to meet the engine’s needs, but above 32 mph the engine needs more
gas, fuel and at that point the engine becomes fuel starved. From what you say though, after the hiccup occurs at 32 mph, then you can go faster w/no other symptoms. I suppose some type of fuel starvation blockage could still be the explanation, but I admit it’s a reach. If you couldn’t go faster than 32 mph, then the blockage idea would make more sense I guess.
10K on a fuel filter isn’t much. It’s probably ok as is. So what else? Maybe the clutch is slipping a tad right at that speed? Possible if some grease or oil has somehow contaminated it. You could ask your mechanic to do the standard test for slipping clutches. Since it happens w/slight accel, that would be consistent w/a slipping clutch. But it would also be consistent with loose/worn engine or transmission mounts, so good idea to ask your mechanic to check those too. Have the mounts every been undone or removed? If so, maybe they were not torqued properly when re-tightened.
The good thing w/a TDI is you know it isn’t the ignition system. But it could still be some intermittent electrical problem of one sort or another. Ignition key, fuel pump relay, etc. And with diesels I’m always suspicious of the injector pump with drivability problems.
Besides the above, make sure your shop checks all the TSB’s and recalls. Other than that, you may have to live w/it until it becomes frequent enough that it will reliably do it for the shop to observe.