I thought it might be a sign, my model Y also does this, every morning I make my way to work, on that spot. So always disengage autopilot or ACC.My car (both my S and the previous 3) and my neighbours car also stutter at the same point on this part of the m4. travelling eastbound you go up the hill, past the first speed cameras and then before the next bridge (cutbush lane?) it tries to stop. Think i've worked it out that the car spots a roundabout sign on the road to the left of the motorway and takes a while to work out it is not relevant. while it does that it slows considerably. That all said Wed night it drove the section with out a stutter for the first time in 4 years. have been oin v11 for a while but had mcu2 put in todat - will try it next week.
I'll have a look now when I next drive in! Going to quick look on Google maps too.
Edit**
You were right!! The sign is visible for the roundabout!
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