@MBB819 I assume you created a new Deco network for the XE75, instead of adding the XE75 to the existing Deco network.

In that case, the M5 must blink blue before adding them to that new network.  You can usually do that via the app.  If you cannot manage anymore the M5 via the app, you can simply physically reset the M5 (Press the Reset button on the bottom of the Deco unit for 1s to reset it)

  @yves_b Thank you! I mistakenly thought that unplugging the unit and plugging it back in was the same as resetting it. I didn't even see the reset button. Much appreciated!