Words containing apostrophes are not recognized by the spell checker. Examples: 
- Some contracted forms , for example "they've"
- A lot of common French words, e.g. "Aujourd’hui", "qu’une", "n'est"

The issue could be observed for the single straight (') as well as for the smart (’) quote.

Workaround:
Add the all word parts to the dictionary, for example, to recognize "they've", both "they" and "ve" should be added to the dictionary.

Fix available in LIB Version 2017.3.1009.