What are the reason Blocked Call Caused" SIP invite failure" in VoLTE?

Hi Experts.

I’m new in VoLTE.
During Drive test we faced blocked Call during inital → one blocked cayse is “Dial serving stop” and other Blocked cause is “SRVCC handover fail”. What are the reason of these caused?

What are the reason Blocked Call Caused" SIP invite failure" in VoLTE?

Did you get this message in DL from P-CSCF after sending SIP INVITE in UL?
After how much time from SIP INVITE you get " SIP invite failure"?

We received “Log Configuration Modified” msg just before call blocked.