You have many customer segments.
One of the segments that is in decline is the "1x Existing Buyer" segment. These are customers who purchased just one time last year, and were existing customers (i.e. were not acquired last year).
Healthy businesses are able to grow loyal buyers. They are also able to grow infrequent buyer segments.
We're conditioned to look for decreases in loyal buyers as a sign that we are failing. Look at 1x Existing Buyers ... declines in customer counts in this segment represent a leading indicator of future business problems.