help. wireless connection often gets dropped.

[lds5618]

I have two computers using modem and wireless router. Sometimes computer A cannot use the internet while computer B is still working. Sometimes computer B cannot use the internet while computer A is still working

One of them often gets dropped although it shows a full signal. I have to restart the router, then it can work again.

It’s really annoying. I'm confused and frustrated.
Hope you can help me. Thanks a lot.

Besides, my router region was set to Asia. But I'm in US. I cannot change it. I cannot drop the list. the other options are locked.