You may travel before submitting any documents to your attorney in regards to your H1b petition. They need to submit your latest documents. I guess, the reason they say that is, your I-94 changes, when you travel. So, make sure you submit your latest I-94 (after you re-enter USA in Jan 2018) while submitting your H1B petition. Other than that, I don't see a reason.
Please call your attorney, and check with them, as to why they sent out that email and update us here on what reason was given by them.