I cleared the Touchwiz data and cache .. so it went to the default configuration. I then started adding my widgets and shortcuts one by one.
I figured out that the Touchwiz fault happens when I add a short cut of an application installed on the microSD card.
I moved all the applications from the microSD to the internal memory and now Touchwiz works fine.
Now going to the microSD. The microSD I have is Transcend cat 10. It should be quite fast, and it is actually fast (R/W). However, I recall some posts regarding Transcend in-compatibility with new Samsung devices.
I have Galaxy S5 as well... same Transcend type and works fine.... BUT ... There is a Samsung application called User's digest for Samsung (or you can find it in the name of Vitamin's for Samsung).. It has a feature to place some tests to the handset. Both Galaxy S5 and Galaxy Tab S show the microSD card test result as "Disconnected"! ... I didn't care that much on the S5 as it didn't cause any problem, but now I started to care after what happened with the Tab S.
I ordered Samsung 32GB cat 10 microSD... should arrive in a week... will let you know about my experience.