STOP comes on my 2019 C4 Cactus with 1.2 THP 110cv petrol sometimes when going up a hill. I stop, wait a few seconds, restart and go OK.
CITROËN C4 CACTUS

The engine on my April 2019 C4 Cactus just started having this issue. 

Once I started out on a recently cold day. Toward the top of a hill the STOP error message came on, the car power dropped and the message stated that there is low oil. Checked oil, it was fine. Stopped, waited a while, and restarted. All OK the rest of the day. 

This has happened a few more times, even after getting a complete oil change. They inspected the belt that on earlier versions of this engine needs replacement often. It was OK and didn’t need replacement. 

Recently, I got off the highway, after driving 130 KPH for 30 minutes, went up a hill at 90 KPH to pass a truck and bam, the STOP light came on and power was lost. Restarted after a minute or so and all was fine.

What could possibly be the issue? I’ve see others talk about a variable valve timing solenoid that sometime needs cleaning. Does this engine have such a thing and if so, where is it located. (I’ve searched a bit trying to find the answer, but can’t) 

What else could possibly be the issue if it is not the belt, and a new oil change was just performed 10 days ago? Anything other part I can remove and clean out to make my engine work as it has these last four years. (which was great, BTW, for the first 68,000 K) 

Thanks in advance for any advise