https://github.com/cucumber/cucumber-tmbundle

Do you have screenshots or a step-by-step list so I can try to reproduce the problem on my device?

Thanks for letting me know.

Does it work again? Sometimes the iCloud servers do have a hiccup and it starts to work again after some time.

Are you sure this is related to Textastic?

Have you added any folder to the sidebar maybe? I've seen CPU spikes when adding certain folders that change often to the sidebar.

I've submitted Textastic 5.3.1 to the App Store which fixes this problem.

Textastic is still under development and I use it every day myself.