FWIW, I had a friend recently do this and got that phone call. What made this an extra layer of a problem was they had the WIU Wireless module plugged into a separate power source. So when they turned off their power strip- yes, they turned off their main transformer, yes, turned off the AUX power in to the TIU, however, the USB coming from the WIU kept the TIU powered. So when they hit this E-stop, they then had to not just turn off the power strip that they thought they had everything in, but no, another second strip had constant power and due to being a wall wart and plug spacing, that is partially the reason for using a separate strip.
Bottom line- unless you see that power and status indicator in the TIU completely off, it's not reset. Again, given there are actually 3 ways a TIU can be powered (USB - only on an L, Aux, fixed1), and most only know about the 2 (aux, fixed1) can lead to this problem.
Picture was found in this topic by @Sean Fanelli Thered LED in the bottom of the picture.