Hi @stitch-bb8,
Thanks for reaching out.
The blue bar for POST measures the time from when the XMLHttpRequest.send is called until the request's ready state changes to DONE. The space that is indicated by the orange line could be processing/parsing that is done on the server side before the Java agent captures the transaction (e.g. a middleware).
Regarding the red line, it depends on the application. for example if you're using angular's http service then there might be some processing that happens in the framework. The best way to debug these would be to use performance.mark and performance.measure (or create custom spans) in places that could introduce this delay.
Let me know if you have any other questions.
Cheers,
Hamid