Brake Sensor problems of the 2017 Toyota Prius

Since purchasing the vehicle in October, 2017, I have had intermittent occurrences where the brakes feel like they slip when coming to a stop. It has happened in all weather conditions, (but mostly when wet), and at all speeds. I can go weeks without an occurrence, and then it can happen several times in a week. It seems to be completely random. I have been to two dealerships, and finally was able to drive with a tech who felt the "slippage". They kept the car for a few days and told me they talked to corporate and that a bump in the road triggers an abs sensor to fire, causing the abs to kick in. They also told me tire pressure might affect it. None of this sits right with me because it continues to happen. I have experienced driving a car when abs kicks in, and this is not the sensation I am getting in the Prius. "slipping" is the best adjective I have to explain what it feels like, and when it happens it is terrifying. The last time I took the car in to have them look at the brakes again, I was told that since corporate had been contacted previously, they would have to go back to them. They didn't keep the car, and told me they would call me back when the corporate rep would be there so he could drive with me. That was a few weeks ago, and they haven't called back, or returned my call. At this point, I feel like Toyota is hiding something from me and I have lost all trust in the brand. I feel like I am driving an unsafe car and Toyota is ignoring everything I am saying to them.