Using Google->More tools->Developer tools (Ctrl+Shift+I) a 404 error was found. The additional script error is due to the the timeline window not populating correctly.
Every example on simile-widgets.org has a 404 error except Compact Painter which has a 410 errors due to missing graphics files.
The problem appears to be a bug because history.html cannot load in either version 2.3.0 or 2.3.1. There are some differences in the dates between 2.3.0 and 2.3.1 when used with TNG.
Version 2.3.1 is available on Github with a change file stating "Version pre 2.4.0". The download below contains the library files and is configured to use local resources instead of static.simile.mit.edu or api.simile-widgets.org. The files use the correct file name and path which should solve the blank screen issue. You can view version 2.3.1 on my genealogy website.
The timeline_231.zip file can be used by anyone that wants to run timeline. All files must reside in the timeline_2.3.1 folder, otherwise you could have a blank timeline window. For instructions please check simile-widgets.org. Report issues or check pull requests on Github. The simile timeline user group can be found on Google.
Timeline 2.3.1 was tested on versions v11.1.3 and v12.0.2. (Timeline 2.3.1 does not work on TNG v10)