Hello,
Again thanks for replying and spending your time.
I've tried "Add try-catch wrapping", but it's the same. But I think you're right, this is probably a problem related to another plugin conflict. I installed W3 Total cache and enabled its minify to test, the result is same, strx not working.
And for the strange characters, I've unchecked "Optimize HTML Code" and now it seems to be working fine. I noticed that it was appearing mostly on pages with bold text, just before the <strong> html tag. I have TinyMCE Advanced installed, I tried with disabling it but it was same. so I disabled "Optimize HTML Code". Also like the other topic you mentioned I'm on a MS IIS-server, so maybe this is causing problem.
Thanks again & have a nice day