Translation:We will contact you.
"聯係" is translated as "keep in touch" in another exercise in this lesson, so it seems reasonable to accept "We will keep in touch with you." Unfortunately, that answer is rejected.
I think the "keeping" part comes from 保持。 That's why I think 保持联系 should be: keep in touch and 会。。。。。。联系: get in touch
Oops, there is also this sentence:
Translation: I hope we keep in touch more often in the future.
I think the English translation doesn't really work well and I do see a difference to this sentence because "我们会跟你联系。 " seems to be about them establishing contact. But you're right Duolingo translates "聯係" as "keep in touch" in that sentence.
Keep in touch “保持”聯繫/聯絡
In Chinese, keep means 保持, usually when we say 保持聯繫, we translate to keep in touch. Though, I don't see very much different between them in Chinese, maybe in English they are different. So, in this example, I tend to use contact.