There is a delay between notification sound and notification banner for mail app in High Sierra. How can I fix this? Whenever I receive a notification from mail, I hear the notification sound but the banner shows up 3-5 seconds later. There is a delay between the notification sound and notification banner. This problem is only specific to mail app. How can I fix it? I have tried restarting and some other standard/quick fixes but nothing helped. This issue also came up after I updated to High Sierra. I would appreciate any help!
Had the same issue on a 2017 27" iMac.
Spoke to Apple support....(I have APPLE CARE)

They had me do 3 things:


Upgrade to the latest version of macOS High Sierra 10.13.4 (That alone did not fix it).
Reset the SMC (for my desktop machine, they had me shut down and unplug the machine for 15 seconds instead).
Reset the NVRAM.