Regarding ''Hey Siri'' !!! or Siri

i have iPhone 7 running IOS 12.4.1 less than year old

previously it was fine running with ''Hey Siri'' even being kept idle as well as while using it.

It used to respond immediately on normal mode and also on low power mode

but now all of a sudden it stops responding if i want to rate it it respond from 1 in 7 attempts

i have tried saying it in soft voice , out loud and all of this being only less than 1 meter away from phone in silent conditions no noise from outside my phone mic is perfect during calls/loudspeaker and even audio recording.

at the time of listening it accepts only half of my sentence then immediately starts to execute on that half sentence.

any idea what should i do?

Many Thanks !!!