Interesting one this. Route 9 doesn't mean anything to me personally being over in Bristol, but time loss events while driving are something I've looked into quite a bit.
Few things worth considering:
Onset time - did it happen gradually or was there a hard cut, like one moment you're at point A and suddenly you're further along?, Physical symptoms after - headache, nausea, unusual thirst? These come up repeatedly in documented cases, Other witnesses - even just another driver who might've seen something unusual
The dissociation/microsleep sceptics will always pile in on these threads, and fair enough, but microsleep doesn't typically account for significant mileage gaps with no memory of the road.
I run a Zoom H5 audio recorder in my car sometimes on night drives specifically because shadow phenomena and anomalous events seem to cluster around certain routes near me. Never caught a time loss personally but I've had some odd audio. Worth setting something up if you use that route regularly.
What's the rough timeframe we're talking - minutes or longer? And were you alone? That detail tends to separate the more compelling accounts from the ones that have mundane explanations.
Would be good to hear from anyone else who uses that stretch regularly. Even if you didn't experience anything, negative reports help establish a baseline.