Car Slowed Down On Its Own problems of the 2018 Honda Odyssey

On 30 Dec 2018 as my family and I drove through osceola county, florida, our Odyssey displayed an error message that read, "some driver assist systems cannot operate: radar obstructed. " the temperature was around 70 deg f and it was moderately foggy. The message cleared itself after 20-30 minutes and the driver assist systems came back online. We did not see any such error for the rest of our trip. At the end of our trip, on 3 Jan 2019, when my family and I were just outside charlottesville, virginia, the vehicle proceeded to brake quite aggressively without driver input, as if it were avoiding a collision. It occurred near mile marker 115 on I-64 westbound, on a downward slope at dusk on dry pavement. We were perhaps 1000-1200 ft from the exit itself, well beyond the range of the �extra long� setting on the acc at 70 mph. The only cars in front of us were already at the exit and did not appear to be undergoing any unusual maneuvers. This off-ramp is particularly long at this exit so I would not anticipate that those vehicles just entering the ramp were decelerating rapidly. I was using acc and lkas, as I had during most of our trip. When the van was braking, I instinctively depressed the throttle pedal to try to maintain speed. That resulted in the engine revving and no change to the hard braking. I disengaged the acc using the �cancel� button and that appeared to end the hard braking (I may have briefly depressed the brake pedal at the same time but cannot be sure). I will also estimate that we went from around 70 mph to around 30-40 mph in those 2-3 seconds. There was no obvious external reason for the emergency braking maneuver instigated by the Honda's onboard system. This presented a significant potential hazard. We were very fortunate that there were no vehicles immediately behind us or we would have run a very high risk of rear collision.