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Quickly new beta! Yes problem is gone!
Every first launch of Textastic. iPhone SE. Latest iOS/Textastic Beta
I think Textastic already has built-in Sublime Text Symbol Definition for sublime-syntax files from PackageDev, but it is based on YAML and works correctly unlike Json-based files
It's custom syntax from Sublime Text PackageDev repo. All json-based files like sublime-color-scheme, sublime-completions,
sublime-menu etc, have a black-colored braces, commas and some comment lines.
If you insert whitespace characters after them (see gif), they are highlighted correctly.
For example, for sublime-color-scheme, you can choose to define the sublime text color scheme syntax
Please keep an eye at some json-based syntaxes from PackageDev
Strange things with curly braces and commas.

You Rock!
Sent! But i have this bug with 'built-in' css.json

At this moment you try MagicPython with custom tmBundle.
Great news, can wait for new betas or release!
Customer support service by UserEcho
There is also a bug associated with the folder name containing characters like ()! + etc. This happens when you create/upload a folder on the webdav server. Tested on Yandex, Cloud.Mail.ru and Dropbox via DropDav service