It appears that I have been experiencing the same issue, Siri will not initialize when using either the Menu or Task Bar icons and has not responded to Hey Siri since the second Beta of Mojave. Everything seems near perfect upon installing the new Mojave (developer releases), although on day three or four everything started to go downhill with errors and things “not working right”.
It started with issues focused around Siri, then problems with Indexing, several other issues here & there and today Siri "does not know who I am”. That is a new one…