Thank you for trying EmEditor Professional!
I reproduced your issue, and the problem was the Line Comment (–) has more priority than multiline comment (–[[…]]). If you remove the string (–) from Line Comment text box in the Highlight (2) tab of configuration properties, it works. I am not sure if I can correct this behavior at this moment.
If you want both types of comments highlighted, instead of specifying — in the Highlight (2) tab, you can add — in the Highlight (1) tab, check “Highlight Right Side”, and select your favorite color (1 – 10). You will also need to remove the already defined keyword (-) from the list.
I hope this helps.
Please don’t hesitate to ask me if you have further questions.