For those having slow/buffering issues on occasion, maybe can try this work around:

a. Disable IPv6
b. Change DNS server

For #a, I know TM IPv6 been out awhile already. The issue is they give out dynamic /64 IPv6 address. You will notice connection buffering/loading when your internet connection auto-redial because the old IPv6 address is still in cache and OS will not switch over to new IPv6 address immediately. OS will cache old IP for around 5 minutes more or less. After that your connection will resume as per normal.

The fix for this is for TM to assign a fix /64 address prefix to each customer. This will also make IPv6 LAN network renumbering easier.


For #b this is pretty obvious already and hopefully you have already done it.

Cheers.

Before calling technician over to your house, here few things u can try to isolate the issue:

1. Connect only 1 phone to Wifi. Other clients disconnect from router/wifi.
2. If using Android 9+, go to Settings and look for Private DNS. Set it to one.one.one.one or dns.quad9.net and save.
3. Open browser and go to https://ipleak.net/ to check DNS Addresses is not using ISP's DNS servers.
4. Run speedtest few times to confirm speeds.

Similarly, you can do these test with only 1 PC/laptop connected to the router to confirm your suspicion.

If you are satisfied, connect back 1 device at a time to router until you notice the problem happening again.(Buffering,slow)

The test should be done with and without IPv6 enabled in router. Good luck.

Common one's are 1.1.1.1, 8.8.8.8 and 9.9.9.9. Then go to ipleak.net to check DNS Addresses not using ISP's DNS.