This is now fixed in Textastic 10.3.1 which was just released.

Do you see any other file extensions that are affected or is it just ".ts"?

Thanks a lot for letting me know about this issue. .ts files seem to be indeed interpreted as MPEG stream files instead of TypeScript.

As a workaround, tap and hold the file to show the context menu and select "Open as text file".

I'll prepare an update with a fix soon.

In Textastic 10.3, which was released today, you can now set the minimum and maximum TLS version for FTPS connections.

If you encounter the "partial upload" error while uploading files using FTPS, please try setting the maximum TLS version to 1.2 as a workaround.

Status update regarding the partial upload issue when using FTPS connections:

I'm working on an update that will let you set the minimum and maximum TLS version when connecting to FTPS server. Lowering the maximum TLS version from 1.3 to 1.2 prevents the partial upload issue mentioned in this thread.

I reported the issue to the Curl project and I think they are aware of it, but I haven't gotten any reply from them. So, until this is fixed in curl, I'll add this workaround to Textastic.

The bigger problem is that someone might intercept your user name and password that is sent in clear text and would be able to do log in to your server with your credentials. 

There is an online tmTheme-Editor at https://tmtheme-editor.glitch.me

It also has a huge gallery of themes. You can edit and download themes and use them with Textastic. 

See https://www.textasticapp.com/v10/manual/customization/custom_syntax_themes_templates.html on how to add custom themes.

After you open a file, you can set the syntax definition to "Plain Text" in the file properties to disable syntax coloring for files with that file extension.

Yeah, that’s ok on an internal network, but not over the internet. 

Textastic internally uses libcurl for FTP connections. 

I could reproduce this issue on the command line with curl 8.7.1 on my Mac.

It seems to be a problem with TLS 1.3 when connecting to certain FTP servers. When I add "--tls-max 1.2" to the command to limit the TLS version to 1.2, the upload works fine.

An upload command like this results in a 0 byte file on the server:

curl --ssl-reqd ftp://<redacted>.kasserver.com/test/ -u <redacted> --upload-file test.html

While adding "--tls-max 1.2" works and uploads the file as expected:

curl --ssl-reqd ftp://<redacted>.kasserver.com/test/ -u <redacted> --upload-file test.html --tls-max 1.2

I've reported this issue to the curl project at https://github.com/curl/curl/issues/13556

For now I can only recommend to instead use an SSH connection in Textastic if you encounter this problem.