R7000 breaks App Store and iTunes Store

Thank you for all your inputs. The problem is now resolved but it is still not clear what is the reason behind.

Here is what I've done (in sequential order)

1) reboot the router several times [same problem]

2) connect an affected laptop to the Internet directly (bypassing the router) [no problem] Repeated for all affected laptop, all are normal.

3) connect the affected laptops back to the router [same problem]

Up to this point, I thought it could be the issue of the router, so I

4) replace the router with one with different brand and model [same problem]

So the router shouldn't be part of the problem. (of course both routers can be faulty at the same time, but very unlikely)

Then I repeat 2) and 3) several times and after around 2 hours, things are back to normal.

I believe it has something to do with the page of itune and app stores (wrong path for their css settings maybe). I've looked for answers from apple community as well and found a few similar cases a few years ago. According to their record, itunes and app store services at my region were normal during that period of time.

Anyway, thank you for all your inputs. Really appreciate that.