The AndTidWiki app for Android devices makes it possible to edit and save changes to TiddlyWiki5, including working offline without a network connection. Download it here.
Don't use Menu/new TiddlyWiki menu option (it only supports the older TiddlyWikiClassic)
Open the file by touching its filename
Try creating a new tiddler using the new tiddler button in the sidebar. Type some content for the tiddler, and click the ok button
The wiki will be saved, and a confirmation message should appear at the top right of the window
Note: You can save your changes by clicking the save changes button in the sidebar even if you have not clicked the ok button to complete editing a tiddler