After a theme update and latest wordpress (4.9.1) I have 2 probems:
1. The left end right signs on the slider are gone and now there is prev and next at the bottom of the slider.
2. It looks like I also have this problem with the testimonials.
3. The small image with the testimonials is now super big.
Through different machines I found out that the problem is caused by the browser cache. Once the cache is emptied the problem was gone. Off course this i not preferred for frequent visitors as you cannot tell your clients to clean their cache, but for now it works.