I have some troubles with DSL modem as well. It helped me to remove VLAN in the PPPoE settings. With different modem, I have to use VLAN so try some different settings. MTU could also makes troubles.

@DataMeister 

In this case, I think you can try to change the DNS server on the ER605. What is your current DNS server then? I don't know that but you can try 8.8.8.8 or 8.8.4.4

Another test is the Ping command. Try to ping an external IP address, that would show you something. For example,

Then we can see how many packets you will lose out of 200. Hope this make sense to you.

@Yannie - 

In case any one is reading this later...

TP-Link tech support suggested I test if the problem is present in the following scenarios:

• The un-bridged modem handing a regular dynamic IP to the ER605.
• A PC connected straight to the bridged modem (Windows PPPoE connection).
• ER605 in stand-alone mode with PPPoE connected to the bridged modem.

I factory defaulted the ER605 and then all the above scenarios tested fine. So I finally re-adopted the ER605 into my controller and suprise it now works fine.

I have no idea how this fixed the problem, because I already tried a factory default and re-adoption sequence after first seeing the problem (before starting this forum thread). Third time's the charm I guess.

The only real differences I can think of are perhaps factory defaulting my modem to get it out of bridge mode for testing, and then re-bridging it. Or possibly the fact that this time around the controller seemed to have all the settings memorized from before. Last time after re-adoption I had to update the LAN subnet because it wanted to revert to 192.168.0.x after I had configured the ER605 in stand-alone mode to use something different.