OK. I think I can help. My January 2017 Octavia Estate SE Sport 1.6 TDI had the exclamation mark problem. To be specific, sometimes on starting the engine the exclamation mark was present (and the cruise control would then not work), sometimes it wasn't present (and the CC would work perfectly). The CC never switched itself on or off while driving: in other words, once the exclamation mark was present, it staying on until the next engine restart, when it was a toss up as to whether the restart would clear it. Excellent dealer (Wings in Peterborough) spent many hours trying to solve it but no error code made their life difficult. The UK Technical Support folk (at Milton Keynes, I think) suggested a stalk change - which didn't cure the problem. They then suggested that the dealer should check for low cranking voltage, which was found. Battery changed under warranty, I believe to a different type. Part number is 000915105FC. Problem solved.
SInce Tech Support now knows about the solution, your dealer should be able to get it sorted out for you at no cost if still in warranty. Good luck.
