There are lots of variables here which make it impossible to answer the question accurately and in detail with the information given, but in short, Yes, your estimated and actual power can differ a lot.

The easy thing to do is just not worry about it and get adjusted to the new, real power numbers. Provided you’re doing the work, it doesn’t really matter what the output units are, watts or Martian blips. Most importantly, though the power meter is an actual measurement of power and not an estimation, so you can more accurately tune your training by eliminating all of the variables which come with the Zwift estimated power.

If you want to dig into why they’re different, I’d point you over to community.zwift.com where you’ll find several years of discussion on the matter. You’ll find, among many things, that saying you can usually “maintain” X-number-of-watts is virtually meaningless without defining exactly what “maintain” means in terms of conditions, duration, and assessment.

Make sure your power meter is calibrated, make sure your bike is properly installed on the trainer (esp. tire inflation and roller pressure), and you’re good to go. There just isn’t a great likelihood that your PM is faulty, so that’s what you’re working with and you might as well get used to it. If the workings of Zwift estimated power are important to you, go ahead down that road, but it doesn’t have anything to do with your power meter.