What should I do if there is always a delay in receiving QQ messages on my iPhone 6plus?

Delete the software and re-download it, enter the phone settings

General

Restore

Restore all settings, and then restore the network settings. If it still doesn't work and you need to flash your phone, you can go to customer service or you can flash your phone yourself.

Download iTunes

Back up the data

Then click restore. It takes about 30 minutes to download the firmware

8M network speed

It takes 10 minutes to flash the phone