thats what happened to me! Was putting down 300+ watts and the meter was showing something like 80W and I was like WTF for about 3 seconds 
Electronic parts warranty/availability - no idea. At some point I started bringing my Garmin bike computer to the gym and pairing to record rides (in parallel to the bike’s head unit). Later on I started recorded using TR app on my iPhone - for example this one: What workout did you do today? (2018/2019) - #5937 by bbarrera was recorded using TR mobile app.