Scripts in EO Browser are passed to Sentinel Hub service using "GET request", which is limited in number of characters, depending on the browser used between 1.000 and 4.000.
But there is an easy way to work around this:
1. Upload your script to some publicly accessible web-site, for example GitHub, like we do in Custom Script repository. E.g. LAI script.
2. Select "Use URL" and paste the URL to the script in "Script URL" field
3. Click Refresh