Whatsapp cellular connectivity issue

Anyone experiencing connectivity issue in Whatsapp while in cellular network? While app is running in foreground, there is no connectivity issue. But when it is in cellular network, incoming messages may or may not come; they will start to come once app is run in the foreground. There is no such issue when phone is connected to wifi. I have made sure background data is not turned off for Whatsapp (for cellular network) nor background data is restricted. There are no issue with viber, facebook messengers. I thought it was because I had my phone rooted. Recently I re-flashed stock and did not root but problem didn't go away.

910H
5.0.1