Apple India — waking of incoming call display

For the last month, i am facing the late waking of incoming call display issue.
The complaint of the issue was registered in feb 2018. According to the suggestion made by apple advisor, i was submitted the mobile to service center on july 2018. By them, they installed the updated os 11.4 and kept the mobile for two days of observation. I was thinking the issue may be solved. Btw, the issue is not solved and again i resubmitted the mobile to the service center.

No words to say. Worst experience ever.