I agree in this case that then OP describes it seems like it was wrong to be showing a lower speed limit. That said, it’s still your own fault if you don’t comply with it. It only makes them money if you don’t comply with a simple instruction. Do as it says and they won’t make money out of you will they?
The problem is always people don’t want to keep to a speed limit or obey other road signs if THEY can’t see a reason for it.
I was going down the M6 the other night and in the opposite side I see highways stopped in lane one. About half a mile or so down the road I see the speed cameras flashing at drivers. I look in my mirror and lane 1 is showing a red X then lane 2,3,4 is showing 40. I bet those drivers going through and getting flashed couldn’t see a reason for it being 40 themselves so thought nah I’m not keeping to that limit. Little did they know there are people a little further down the road in a lane.
Often when a speed is left up and there’s nothing there, recently there probably has been something like that or a work force in the lane and control need to wait for confirmation it’s safe before clearing the signs.
Just because drivers can’t see a reason for it doesn’t mean there isn’t a reason or wasn’t recently.