has any one experienced cruse control bad function.
when set it some times unlock the selected speed, and the only way to use it again is to stop the engine.

No, Mine works fine  2013 Discovery HSE Luxury - 3.0 SDV6 - Santorini Black
2013 Evoque 5 Door Pure Tech SD4 - Orkney Grey with Panoramic Roof (Mrs E's new baby)

GONE - RRS - 3.0 TDV6 HSE - Santorini (2010)
GONE - RRS - 2.7 TDV6 HSE - Java Black (2007)
GONE - Porsche Boxster S - 3.2 - Black

It may just need a software update or something like that get it in to the stealer's mate RRS TDV6 Gone but still around
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I love boobies i love boobies i love boobies cuz i'm a big kid now! (Come on everybody sing with me you know the words!)

... Or you may need a new circular cassette rotary coupler in your steering column.

I know, it sounds like a fake gadget from a Back to the Future movie... But it is an actual part and it is the most likely cause for the cruise control failure you are experiencing. A couple of RRS owners on rr.net had those contacts replaced under warranty after their cruise control set / resume buttons failed to operate a few times.

PS: Welcome to the forum! 

umbertob wrote:

... Or you may need a new circular cassette rotary coupler!

AYE CAPTAIN and the Dilithium Crystals are breaking doon - She just kanna take anymore!!!!!

Sorry Umbertob, Just couldn't resist it! It just sounds so "Star Trek"  2013 Discovery HSE Luxury - 3.0 SDV6 - Santorini Black
2013 Evoque 5 Door Pure Tech SD4 - Orkney Grey with Panoramic Roof (Mrs E's new baby)

GONE - RRS - 3.0 TDV6 HSE - Santorini (2010)
GONE - RRS - 2.7 TDV6 HSE - Java Black (2007)
GONE - Porsche Boxster S - 3.2 - Black