I am new to Zwift and had fun completing the intro workout. Using Garmin Speed and Cadence sensors with my Cycleops Super Magneto Pro traditional trainer. Things worked well for my first workout, but ever since I cannot get the appropriate watts to show up. My sensors are connected and I’ve selected my trainer just like I did before my first ride. When selecting my speed sensor it shows an appropriate speed with me pedaling (ex. 15 mph) then when I start a training session it has me barely moving (3-5mph or less) and low watts even on 0% grade road. Any suggestions? I am running this from my iphone 7
You really should get a real power meter or a smart trainer for using Zwift
Did you select the correct trainer? Correct resistance level.
Also check that the speed and cadence sensors are not mixed up.
Yep, confirmed all of the above. Like I said, it worked perfectly for my test ride and now doesn’t. I tried re-installing the app too, still no luck 
Thanks for the advice, Ed. Figured this way I could get started for $70 (cadence and speed sensors) instead of $700. Hasn’t turned out to be a very good test run since I only got one shot at it! lol
Lets see if I can help a bit. Zwift wont show the same speed as your cycling computer. Zwift calculate your in game speed or virtual speed from a your trainer power curve. So depending on your trainer I would guess that you should see about 100w-200w at 15mph.
That’s what I was getting on my test ride. Now it shows anywhere from like 0-80 watts. I have checked and confirmed that my speed sensor is actually my speed sensor a few times. Most of the time it’s giving me wattage somewhere in the mid-teens.
Do you have a bike computer to check if the speed sensor is working properly, it can happen that the magnet have moved and it only pick up every second revolution.
Also try to disconnect your cadence sensor from the bike and try again.
Another thing, check that you selected the correct trainer in the paring screen. Unpair everything and repair.
Also, try a new battery and see if that resolves the issue.
Check your tire pressure and tension on the trainer barrel. I have the same set up as you and find that if my tire pressure is too low or and barrel is not adjusted properly I have issues like this.