"I've never been able to find any engines via the app on the 2nd loop, only the first. I was told in order for the DCS to find and engine initially, it has to be the only engine on the track. True or not?"
The first time you ADD an engine to DCS, it usually finds that engine much more easily if the engine is on the track by itself (people make separate programming tracks just for this purpose). Once you add the engine, you should be able to do a "Read" on the remote, or a "Refresh" on the Ap to find it, even with multiple PS2PS3 engines on the track (it should find all of them). This assumes that the engine had a good, charged battery/capacitor in it when it was originally added and so retained its new DCS identity (the number usually changes from the stock, factory "1" to the number of the next available slot in the remote).
"As I said, both loops worked at one time via the app but now only one works. I run the 2nd loop via the hand held remote and it runs fine, I just prefer the additional options and ease of the app."
I don't have enough knowledge to answer this one-perhaps Barry or one of the other Guru's will chime in. I wonder if the DCS signal is turned off on the second loop in the Ap, but is on in the Handheld.
Just out of curiosity, what happens if you roll the outputs of your DCS Fixed Channels so that the first loop is on Fixed 2 and the second loop is on Fixed 1? Do both still work with the Handheld? With the Ap, does the first loop stop working and the second one now work?
"In addition, I had a TMCC base wired at one point and was able to discover and run a Lionel TMCC engine via the app, but that stopped working suddenly as well, so I disconnected it and no longer run TMCC (I don't have a Cab-1....yet....)"
I don't, at present, even have a working Cab-1. I have had one for years, but rarely use it (almost always running TMCC through the DCS Handheld because, for me, it is easier than the Cab-1 and, more recently, through the Ap, which is easier still (for me)). There are some things, I understand, that are easier to do with the Cab-1, but I can't remember what they are.
You really shouldn't be able to "discover" a TMCC or Legacy engine via the DCS Ap. There is no two-way communication with TMCC/Legacy engines, so DCS, regardless of whether you are using the Ap or the Handheld, does not know there is a Legacy or TMCC engine on the track (unlike PS2 and PS3, where a Read/Refresh will tell you which engines are active). You have to either have left the Lionel engine on the active list, and not have done a Refresh, or use "Edit" to move it to the active list to run it in the Ap.
TMCC should not affect DCS operations (other than there are some TMCC electronics that can kill DCS signal strength-people used to put chokes in these TMCC locomotives to alleviate this). The connection is one wire to the outside rail of both loops. If you have a common ground on your layout, all you have to do is to run it there and TMCC will work. Your transformers have to be phased to do this.
The two ZW's on my layout are in phase and have common ground, so I only had to run the TMCC wire to one place to have TMCC on the entire layout.
"I didn't alter any wiring or tracks..the 2nd track and TMCC just stopped working."
It seems to me that there might be something interesting going on with that second loop. What happens if you move the TMCC locomotive to the Active List with the Edit command, can you run it then?
Have you consulted Barry's book regarding wiring and connecting both DCS and TMCC? It makes all of this very, very easy.
