I’ve noticed this a few times when using my iPad to run Zwift. I start my Garmin at the same time as Zwift, and most times both keep the exact same time. Today, I noticed that the iPad lagged behind my Garmin & lost over a minute by the end of the 1:20:00 workout. The workout countdown timer was accurate.
Look at my pics, you can see that the Garmin & Zwift timer are different. But if you factor in the workout countdown timer, it lines up with the Garmin.
This difference increased throughout the workout.
Something to do with Apple. This happened when I used to use Apple TV. When I did a workout the elapsed time and the workout timer would slowly drift apart. Now I use a PC and the times stay in sync.
This is interesting because I saw this regularly with my 5th Gen iPad. Recently,though,I changed to a 9th gen iPad and I never see this anymore.
I haven’t Zwifted on an ATV for a while now, so I can’t say if it happens there, or not. My guess has been that the issue was related to something starting to ‘fail’ due to the age of the device, but I really have no idea.