This is one of the most common issues that happens to Oxygen Builder users. Post migration, be sure to follow these steps:
**Resigning shortcodes will fix this "broken" appearance 90% of the time.
At this point, the frontend issues should be fixed. If they persist, open up each page/post/template in the Oxygen Builder, and click the blue "save buttons".
For additional info and screenshots, here's a great resource: https://isotropic.co/3-steps-to-resolve-99-of-problems-with-oxygen-builder/