Hello,
I have a similar problem.
I created groups and nested repeatable fields in a custom table without issues.
But now at once, if I add a new textarea, when I try to save, all field settings are lost.
Here is the JSON export before adding a new textarea:
https://drive.google.com/file/d/1vUuuLUHqZ6ZsOLhz5lX0sGSu-fDdXgLN/view?usp=sharing
My thought is that some textarea field settings might be corrupted, but I am not able to track it down.
I even deleted the custom table in MySQL and let the plugin recreate it automatically, without luck.
Please help, because the main reason I purchased the plugin is to speed-up development and this issue is causing delays on my milestones.