2G/3G Phone calls no longer possible on 4.6.0.15 (XA2 Plus & X10 iii)

Bug Reports
21

I had several awkward yet isolated issues with Inbound calls in X10III, which share some traits :
4.6.0.13:

  1. Delayed ringing: I picked the call right on, yet -according to the caller - after a long ‘ringing tone’ period
  2. No ringing at all , no unanswered call nothing.

4.6.0.15:

  1. Mobile phone started ringing while I was picking the call on the fixed line (same caller!). The caller gave up the call on the mobile line due to no answer.

It’s not reproducible so no bug report. The switch on 3G/2G for voice call works fine in general.

VoLTE is disabled (device not supported by the mobile operator).
All that happened while at home, with strong 4G and 5G coverage.