@Vincent-TP I have a controller that I can't restore, I've tried on several devices with both windows and linux servers but it fails every time. It looks like all backups from 5.15.20.7 and up are...

@lkakas I don't have any more suggestions for you, so we'll probably have to wait for TP-Link.

@lkakas I don't really know what it could be, is it possible to remove the ISP modem and connect the router directly to the internet? I have done that so I get internet directly on the ER8411

@lkakas That doesn't tell me anything, but are you using a controller or is it stand alone? Either way, you can try a factory reset of the router, if it is stand alone, you can take a backup first if...

@lkakas Well then I don't have a quick fix for you, let's hear what @Clive_A says about this.

@lkakas ok, yes then it seems strange, I have an ER8411 myself but haven't had the same problem, have you tried changing the network cable? I use SFP+ WAN1 for internet but have previously used...