Unfortunately, J6 looks like suffering from an underdimensional antenna e.l ..
When I set up our J6 side by side, on a table with a Huawei top model against the same Telia antenna / operator, J6 got only half the strength of the signal while Huawei was full.
This can explain why the phone is still breaking conversations. Strangely, it did not happen in the first few weeks, but after some updates of the software.
Sorry folks, avoid this phone until Samsung can deliver a better product.