I did this, it's accepted. April 13 2018
I would expect that I should be able to use "我一會會跟一些同事吃晚飯。"， "我一會兒會跟一些同事吃晚飯。", and "我一會會跟同事吃晚飯。", but all are rejected.
Shouldn't 几个 be allowed in the translation because of "some"? (i.e. 我一会儿会跟几个同事吃晚饭)
Yes, and, to be more polite, you can also use 几位.