How does the styling around the problem area look like? Maybe there is a span involved or some kind of whitespace?
If so, you can adapt the search-expression to:
Code:
(?<!St|Mr|Mrs|Dr|<|\d)(<p[^>]*>\s*|\!|\?|\.|…|:)( ?|\s*</?span[^>]*>\s*?)(»|«|“|”|„)?( ?|\s*</?span[^>]*>\s*?)([A-ZÖÄÜ])
It doesn't catch everything though - especially if you have chains of spans or even nested spans or divs.