No problem Mika. But there's no need to leave it open. As luck would have it the third plugin a reactivated was UpDraftPlus and it started again. Deactivated it and it went away. Reactivated and it came back immediately.
I tried it a couple of more times and that's definitely what's causing it here.
By the way, this the premium version of UpDraftPlus I am using, so I don't know if this is the same reaction with the version in the repository, but I imagine it might well be.