Gantry broken

So I was travelling home after work on Saturday morning around 5am there’s usually a gantry above that shows 60mph for air quality so I ideally slow down before that cause I know it’ll show up every time, before getting to the gantry before the speed cameras I noticed there was a problem with the sign, there was about 1/8 of what I could see was a mandatory speed limit, therefore I assumed it was showing the 60mph speed for air quality so I continued on, the next gantry to where it showed 60mph correctly I was still doing 60mph watching my speed as anyone would, but upon passing it flashed me twice, I knew I was doing 60 just a little bit under but quickly looked down just to check and was left confused on my trip home, not sure if it was because there was a van that came speeding up behind me as i went under, but just a thing to check