The lights work properly, then stop all of a sudden
Likely a malfunction of the first light that is off. Try turning the lights off and back on. If problem persists, it’s best to replace the suspect light. However, in rare cases it could also be a data issue between the last light working and the first light off. To avoid making two splices, it is typically best to just replace the last light that works and first light that is off with two of your spare lights.
Only half the lights work and they are unresponsive
Likely caused by positive and ground wires coming in contact. This could either be in a connection or at the terminated wire at the end of the run.
The lights are doing the incorrect color or effect
This is likely caused by damage to the data line either within an LED or between LEDs. Replace the last working light and the first bad light.
The lights are getting dim at the end
If you change your lights to solid white, do they gradually turn yellow and start to even turn red? Sounds like you need a power booster. These are recommended every 75′. but can vary with splits in the line and overall load.