Also in Chrome 58.0.3029.81, my normal browser and tested it also with Microsoft Edge 40.15063.0.0, which I normally don’t use.
Cleared the cache and just with 2 or 3 tabs opened.
Using PHP 7 and kiwitrees 3.3.0, It is on my website, but also on my local testversion.
I had never seen this before the last upgrade.