A few years ago we bought some Christmas lights that can be more heavily exposed to the elements. The hope was to avoid having to restring them every year.
They worked fine for two years. This year when I plugged them in to test them, they worked for a second and then shutoff.
We got out the ladder and one by one tested the strands to find the source.
(Actually we did a binary search: check the first half and second half, then narrow down which group had the problem)
After a few minutes we found that the first strand was broken by popped fuses and all of the rest of the strands were fine. Replacing the blown fuses caused them to blow out again.
The strand was dead with a short somewhere. Probably from a squirrel checking if the lights were edible.
By acting methodical (e.g. disconnect one strand at a time, measure) we were able to diagnose the problem easily. It took more time to test but we ended up saving effort re-stringing a bunch of lights that still worked.
Sometimes you'll have time to be methodical to find the root cause of a problem.
Other times you don't have the time and just need a quick solution for now.
If you're swimming with more issues than time right now, just deal with them for now (run that second set, give the irate customer a replacement, reship a missing package, etc). You can come back after the holidays to follow up on the source of the problem and try to prevent them from next year.
If one of those issues you have is customers not coming back, Repeat Customer Insights might help uncover why that's happening. Using its analyses you can figure out how to better target the good customers.
Analyze your customer's behaviors before they defect
Your customers aren't yours forever. Some might have defected today, never to be seen again.
You need to analyze your customer behavior so you can reach them before they defect.