Darn, you're right. And I finally found my mistake. I thought that I was looking at the unprocessed RAW files in Lightroom but in stead I looked at the version processed by LRTimelapse and later in the proces imported into Lightroom (the workflow you advise and I prefer to use). You cannot see that treatment so the photo looks unprocessed and exposure looks OK. I even used the same workflow with the RAW files I send you (first through LRTimelapse and then import into Lightroom) with the same results.
The original RAW files clearly show the overexposed areas around the sun, especially after a HG step. 

In great shame but even greater gratitude I thank you for your time. I now know what went wrong, I understand it and I can correct it. Still in the process of learning and ruining a potentially great sequence often is a very good tutor!

Thanks again

Simon Plat

Hi Simon, no problem, that's what this forum is for ;-)