I have had a similar experience with my Apple Watch. My cardiologist at Mayo Jacksonville said that the Apple Watch is interpreting premature atrial contractions as afib. I have a PAC load of 10-12% and no afib, and my weekly Apple Watch reports state I have afib anywhere from 7% to 25%. I have tried to "break the code" and figure out why this number changes so dramatically from week to week - I have deliberately modified my exercise routine, caffeine and alcohol intake (always minor) with no effect. The Apple watch doesn't check for afib constantly, so my guess is there is some randomness as to whether someone is having afib, PACs, or in your case SVT when it happens to check. I continue to track my results, but I'm not sure it's giving me actionable data.