My setup is similar and I have no issues whatsoever adding engines to either the remote or the app:
- 3 Rev. L TIUs in Super TIU mode.
- Each WIU is connected via an Ethernet cable to a switch. The switch is connected to an AirPost Express access point which communicates with the AirPort Extreme router downstairs.
- Each WIU is assigned a static IP address (10.0.1.96 - 10.0.1.98) based on its MAC address.
- WIU #1 is connected to TIU #1 via a USB cable. However, WIU #2 and WIU #3 are connected to their respective TIU's serial ports (see below for the reason) via a USB to Serial cable.
The reason I use a USB to Serial cable for two of the WIU/TIU combinations is the following.
I have always had a long (40') serial ribbon cable that goes from the PC in the train room work area, around the layout to where the TIUs are located. When it's DCS upgrade time, I connect the serial cable from the train room to the serial port jumper cable connected to the TIU. I also have extension cables to jumper together the ProtoCast and ProtoDispatch ports. Then I can upgrade the TIUs in place.
When I first began using the app, I connected the USB ports of each TIU to its respective WIU. However, I encountered a situation where when certain commands were issued to an engine on TIU #2 or TIU#3, the WIU would "go out to lunch" for up to 30 seconds or so. TIU #1 didn't have this problem and the remotes worked fine.
After eliminating everything else, to my surprise I found that the problem was finally resolved by removing the long serial extension cable from TIU #2 and TIU #3 serial ports, even though this cable was absolutely a straight-through, 9-pin cable with nothing attached to its other end.
TIU #1 was unaffected, seemingly because it connected to a Legacy command base using an MTH #50-1032 cable.
I now have TIU's #2 and #3 connected to their respective WIUs using a USB to Serial cable with a 2-port splitter for connecting the long serial ribbon cable when its upgrade time.
If you have anything dangling from the serial ports of your TIUs perhaps removing it would help to resolve the problem.
