@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...

@lkakas you should upgrade to the latest firmware, the one you have is old and a lot has been fixed in the last year

@Cdn_Brad use a DDNS provider that is supported by TP-Link, I myself use no-ip which works well with TP-Link. connect to vpn site to site with FQDN

@uguryilmax Are there hundreds of users or is it max a hundred? Hundreds of users then you need an ER8411, if there are max hundred users then an ER7412-M2 or ER707-M2 is enough