Lightroom unusable after update to 6.8

Hi,

Lightroom was runing perfect. It was basic version installed from CD (6.0 or sth like that). I have updated it to 6.8 and after that is unusable slow. In library some catalogues have no number of pictures only 3 dots (...) it takes very long to calculate this count and load images ("loading..."). In develop it takes very long like few minutes to load picture. After picture is loaded lightroom works ok for a moment, i can load other images quickly. But after minute or two it slows down again and cannot load any picture. Whith this update to 6.8 some settings was changed and it stop working. Switching off GPU acceleration dosnt help. it is windows 10 laptop with ssd, pictures are on external drive. CPU and RAM usage during loading is at constant low level (30% and 50%). It was working very smooth just before update.

How to fix this?