Absence of ringing tone

Summary

Since /e/ OS 1.5.1 on FP4 I experience the absence of the ringing tone on some outgoing calls either to a landline or a mobile network. I have neither switched the mobile provider nor the SIM card. Despite it is quite strange to not hear the ringing tone but suddenly the person I have called I prioritize as S4 because dialing and calling is working.

Diagnosis

Components affected

FP4 since /e/ OS 1.5.1

Priority

S4 - low

Has it happened before?

https://community.e.foundation/t/absence-of-a-dial-tone/19805

Solutions

Nothing I know of.

Possible fixes

Nothing I know of.