Yep!!!Brother I got the same issue with my galaxy f12. It's not vibrating recently but when I spank it bottom side(at speaker/charging port) then its working for some time then again its not and its repeating

I got a new update recently may be it is fixed in it... try to update if there is... okay

Okay... I think It may be like u said, but have u tried connecting to wifi

i think it's the sim problem... I'm using s-m31 i got the same problem like you.. Then i have changed sim network then it working properly... although samsung m31 signal receiver is lil'bit lowi think you have to go through changing the network...if ...