As long as you are achieving breakthroughs periodically you should be fine. 
Breakthroughs validate your fitness signature and update it if any change occurs.
The Advisor doesn’t specifically recommend a breakthrough workout but under your name on the home page you will notice “Last Breakthrough:”. Under that is a warning if your signature has not changed in more than 3 weeks. When that happens you should search the workout library for “breakthrough” and perform one of those workouts.
Other ways to generate a breakthrough include Zwift races or a group ride with wind-up sprint or any hard effort that draws MPA down and you force you way past it generating a breakthrough event.
Check out this post and you’ll find many answers and tips which may generate more questions. 
Beginner questions - Support - Xert Community Forum (xertonline.com)
Examples: Let's See Some Recent BT's
Reference: Breaking Through the Xert Way! – Xert (baronbiosys.com)