A few phones are reported here to have echo problems, in my case the Moto G4 Play (harpia). However, these seem impossible to fix and remain in different versions of /e/.
Are some low-level audio processing functions contained in device-specific drivers? Presumably, /e/ developers will not be able to fix such drivers - e.g. looking at the Lineage build instructions, there seems to be a lot of proprietary stuff:
Maybe someone knowledgeable can shed some light on the problem?