@Cadiper 

Check your blacklist/whitelist settings incase you've unintentionally added them to a whitelist and accidently turned the balcklisting on, assuming you use that function.

  @Cadiper 

If those devices are connected to a profile, there's a restriction area amd I believe there's options in there to stop downloads ect, 

Check in there to see if ones active that could be blocking those devices 

  @Cadiper Same issue. Recent occurence, and only when connected to the extension-unit. Main Deco unt operates as normal.
Extender unit can't download from Google-Play or play Youtube videos without massive delays.

  @Bogle I have not set up any black or whitelists unfortunately, but it was a good suggestion. 

Ignore it anyway, it on a second look wouldn't be stopping you anyway.

My last suggestion that is.

I think basboi means in the Tether app if you've given devices rules.

  @Bogle 

Yea I mean in the tether app, 

I've been having wierd things happening on my tether app where I block sites and the blocked site list disapears and even the content filtering keeps unchecking the filters I implement so who knows something might have been activated without you doing it 🤷🏼‍♂️

  @Basboi85 Okay, I havn't used the thether app. And I just tried a factory reset on all de the devices without any improvment on my matter. I'll call my ISP in the coming week to see if they might have a solution. 

  @Cadiper 

Save your time it's not your isp doing.

Read this

https://community.tp-link.com/en/home/forum/topic/267956

If no joy do what I suggest below.

Start like this, download the latest FW for your router and drag the one file out of the folder and put it on a USB stick

Next press the reset pinhole in with a pin, toothpick etc and hold it until the router lights go out and then all flash on, this is to reset the router fresh

Now login using a PC etc to 192.168.0.1 it could be 1.1 or 0.0 at the end depending on the router, one of them will allow you to the set up page, if you get told it's unsafe go back just ignore it and carry on by adding a simple password to begin with while you're setting up.

Next plug the usb stick in and re-flash the FW, doesn't matter if it's the same version or not just let it glide over and put the fresh instructions in, you may be able to use an older one first and then the newest one over the top this ensures the FW has been written over and then re-written again, disconnect the cable that feed the router from the isp as well before you do it.

Let it do it's stuff and once rebooted...

Put your passwords in and turn off UPNP & WPS and try the Play store again, do this before you tweak your settings to help eliminate a config problem.

Other than this are you using a VPN, if you are that should be your next port of call for problem solving and I'd say it's 99% guilty of causing the problem if you are using one and especially if it isn't configured right.

After that I really don't have anymore idea's for you.