Having problem downloading apps from appstore

Hello,

I've been having this problem for a month.

Everytime I want to download the apps, it stuck on "waiting" for several hours until loading to download. The progress of download speed also so slow. I tried sign in / out from appstore, restarting the device but nothing seems works.

This happens both on my iphone XS and 4th gen ipad air. both have 50gb+ free storage. my wifi works perfectly fine. I tried stop the download and redownload again but it still stuck on "waiting" in such a long time. What to do to solve this problem? Please help?