any sample files ?

AFAIK, the second-to-last colon is not segmented because it's immediately followed by a tag, not a space... which confuses the segmentation engine. Or, maybe the space after the tag is a non-breaking space.

The last colon is probably followed by a non-breaking space... which does not match the "\s" rule in .NET (https://docs.microsoft.com/en-us/dotnet/standard/base-types/character-classes-in-regular-expressions#whitespace-character-s)

There is no non-breaking space in this part of the document.

Well, if you say so... Then examine the segmentation rules and the file content yourself and think yourself what could be the problem.
I'm afraid we can't help you then. Only YOU have access to information needed. We don't.

Please, find attached a sample file.4431.sample.docx

That's an AWFULLY formatted document... I bet it was converted from a PDF, wasn't it?!

Clean up and unify the formatting first (e.g. make sure that the switch between italics and normal happens at a proper place) and then it might work.

BTW, why do you want it to segment at the colon anyway?!
That segmentation rule is totally useless for usual documents (including this one)... it's made for direct speech sentences: https://en.wikipedia.org/wiki/Direct_speech. And does not make sense otherwise.

Well, as I know it was originally prepared in Word.

I cleaned it up with TransTools. Do you have any idea about how I could clean it up further?

And yes, segmentation after the colon makes sense in this case and other cases, too.

Please note that the issue here is not whether segmentation makes any sense here or there, but why segmentation does not work in this case!!!

Sandor Juhasz said:

why segmentation does not work in this case!!!

That's now rather a question for SDL, since even after cleaning up the formatting and making the source formatted exactly the same as the first, correctly segmented sentence, the segmentation does not work for the other two sentences...

So it's SDL's turn now.

I agree.