DCC system debugging

First:

Don't assume it is the DCC system or loco! Check your track, make sure you have good power. Next find the LEAST COMPLEX way to reproduce the problem. If you can make it happen on rollers on an isolated track section, debug in that environment.

Test with a different loco

Many people test the system with a loco that has somehow gone defective. If you base the health of your system on one loco, it's usually a mistake. Try a second loco.

Check the system by minimizing the variables

Put the loco right near the track feeds

disconnect other track feed

disconnect the track feeds and power a separate 3 foot section of track

use a different throttle

use a hardwired throttle

check your power supply voltage

Packet analyzers

A common issue is that you get erratic operation somewhere on the layout. Usually it is bad wiring, but occasionally it is something else.

This is where attaching a packet analyzer to the rails lets you verify what you are sending is what is being received. Also, some systems just put crappy data on the rails, poor packet timing, etc.

Pricom

Pricom made a nice portable one, powered from the rails, mono LCD readable in full sun. If you find one of these for sale, buy it! There is some integration with JMRI.

NCE

NCE also made a little module to allow looking at packets. It also seems to be discontinued. I have one, but have not played with it yet, some integration with JMRI also.

Arduino - based

Here's one I was pointed to: https://rudysmodelrailway.wordpress.com/2015/10/23/dcc-sniffer-packet-analyser-with-arduino/