Light gremlin?

[Dorchester2]

Back from Brittany.
Lovely week with 4 days in a row with a brilliant sunshine, cool in the early morning but rather warm enough along the day.
Lots of castles & gardens visited.

My pride & joy was a very bliss during those 2k km (1.3k mls) but...
a gremlin on sentry duty...

That time he was nested in the light electrical system but... everything was fine, all the lights perfectly working but that stubborn message on the computer screen telling me sometime a front bulb was failing, sometime a rear one, sometime the back plate light and sometime all the lights HS!

It first appeared on our first day when going to Brittany, after putting the light on when driving in a tunnel, I don't remember whether it was the first time or not. It lasted a pair of hours then after a few hundreds kms the screen was cleared I don't know how.
As long as I did not use the dimmed / head lights button, all was fine.
Another day back again and the day after without being cleared appearing immediately when I fired up.
The last day of our stay in Brittany, the sky being cloudy in the morning, car colour body being dark and passing through some forest, I kept the lights on the whole day: first the gremlin appeared then disappeared until the end on the day.
However on our way back the weather being chilly & cloudy, I kept the lights on the whole day too: nothing wrong happened even in the beginning, all was back as usual and the problem looks now being cured automatically again... so far.

Where could that come from?
A poor contact somewhere?
But don't tell me it might be moisture: the car was parked in the garage before our trip began and the first 5 days of the week were dry & shiny. Never the lights did that before but the last time several weeks ago when the left dimmed bulb was actually dead, which was normal.