First, Siri is having problem with some commands. Sometimes it responds but not following the command and sometimes it crashes.Take a look.
https://pbs.twimg.com/media/CHIW2kTVAAAhW2J.png
Second, Siri button on Assistive Touch is disabled while on the home screen even Siri is enabled, Take a look. https://pbs.twimg.com/media/CHIWjpUUgAA1apm.jpg
Third, As I said earlier Siri button on Assistive Touch is disabled but this time while using Siri. Take a look.