dial *#0011# and check which band your network is connected to.if you're
using jio and Connected to band 5 than you've to change it to band
40.check if its need to be changed then i'll tell you how to change this
band if you want.
i am facing this problem since February update. i did almost everything,
factory reset, visited service centre many times but nothing changed.
This problem is persistsing in the update which Samsung is not solving.