Migration was fine. Database. Content. Plugins. Theme. Theme Settings. Etc. All migrated just fine. After migration, the front end and backend of the site appeared normal.
The Pro Editor was corrupting pages when I edited them. The simple act of selecting “Edit with Pro” on any page would break it. This was the issue.
I’ve fixed the problem myself. I took several hours and exported every single page, post, and global block from my staging site as templates. Then overwrote every page, post, and global block on my production site with those templates. Just simply re-feeding Pro Editor these templates alleviated all CSS issues. I’m still unsure as to why this happened in the first place, but happy I’ve found a solution. I can now select “Edit with Pro” on any of my pages and not fear destruction of the page.
To be clear, I wasn’t asking for help to migrate my site. I was just giving recent history of the site for context. I was asking “why is the Editor breaking pages.” Apologies if I was unclear. But it’s done now. I fixed it on my own. I feel I’ll be hesitant to reach out for support here in the future, which is unfortunate. Perhaps my opinion will change if I happen to face additonal issues in the future.
Know that I truly love X and Pro and have been using it for years across many projects and clients. This was just a fluke circumstance which I’ve never encountered, and unfortunately still have no answer to as why it happened. That’s the way it goes though sometimes! Carry on. Thanks for trying to help!