After some time of inactivity, the smartphone stops making and recieve calls, as well as USSD. Turning on airplane mode or rebooting makes calls work.
At these moments system can't switch from 4G to 3G mode to receive or transmit 3G calls. (when i switch preferred mode from LTE to 3G, it shows as unavailable until i switch airplane mode). Network works fine in initially preferred 3G mode.
After some time of inactivity, the smartphone stops making and recieve calls, as well as USSD. Turning on airplane mode or rebooting makes calls work. At these moments system can't switch from 4G to 3G mode to receive or transmit 3G calls. (when i switch preferred mode from LTE to 3G, it shows as unavailable until i switch airplane mode). Network works fine in initially preferred 3G mode.
Blackview a100 / MediaTek Helio P70 (MT6771T) / Vendor A11.