Computer error

#1
On two different bikes, Cannondales with Steps, we have had our "computer" reset to a previous reading. For instance, yesterday it should have read 51km at the nd of my ride but when it reached 46 it reset to 36. The total distance also went backward. My partner's bike also did the same a couple of months ago. Any ideas?
 
#2
Are you also using a gps tracker placed near the computer? I have had problems with a DPC 14 on my Bafang system and the retailer suggested that my Garmin 130 might be interfering with the computer. True or not - I don't know?