Estel, already investigated deeper? Or reflashed?

Today I think I had exactly same behaviour, no call-ui came up, no call came through. Did not check about modest, as I needed phone functionality and did a reboot (before I remembered you and your prob).
After a reboot everything was back to normal.

As I still switch between SIMs and also have a high swap usage I sometimes have the feeling that 'some swap thingy here goes crazy'.
Please check your swap partitions or disable extended swap / enable stock swap partition and test once more. [a shot in the dark]