The NIV footnotes indicate that some early manuscripts do not have "in Ephesus" in then. The NET has extensive notes on this, but they only state the the earliest and most important MSS "omit" the words. They go on to suggest a scenario in which copies may have gone out with a blank line for Tychicus to fill in later.
What do the MSS look like? Is there indeed a blank space or line in these manuscripts or do the words run together simply omitting the phrase εν εφεσω?