kind of vague but I guess you wanted to be brief so some options might be:
1. Factory default restore / minimal router setup - use LAN not wireless, no torrents, usb drives disconnected, VPN off
2. Turn off IPV6 and use IPv4
3. Re-verify and then verify again there is no Windows firewall or Antivirus firewall blocking on PC, or if game console no Trend Micro AI Protection blocking on router
4. revert to an older version Merlin router software (because miniupnpd has been updated, below)
Code:
http://asuswrt.lostrealm.ca/changelog
380.58 (20-Mar-2016)
- CHANGED: Updated miniupnpd to 1.9.20160222
380.57 (24-Dec-2015)
- CHANGED: Updated miniupnpd to 1.9.20151119
378.56 Beta 1 (12-Oct-2015)
- CHANGED: Updated miniupnpd to 20150723 snapshot
378.54 (7-June-2015)
- CHANGED: Updated miniupnpd to 1.9.20150430
378.52 (3-Apr-2015)
- CHANGED: Updated miniupnpd to 1.9.20150309
376.48 Beta 3 (02-Nov-2014)
- CHANGED: Updated miniupnpd to 20141023 code from Github
376.44 (3-Aug-2014)
- CHANGED: Updated miniupnpd to Git head (as of 20140731)
374.43 (6-June-2014)
- CHANGED: Updated miniupnpd to 1.8.20140523
5. Turn off NAT acceleration
6. Restart the game console or PC to renew all open ports
7. This is the changelog for miniupnpd:
https://github.com/miniupnp/miniupnp/blob/master/miniupnpd/Changelog.txt , which may or may not give you some new ideas to try but worth a look
8. "Respond Ping Request from WAN" turned on, maybe give it a try although it should make no absolutely no difference
9. For testing: I would say compare with any other games that requires open ports. If none of them work I would plug the console directly into the modem. If on PC then don't do this without a firewall/antivirus
10. If on PC then grant exceptions inside your Antivirus and firewall rules for the game process and launcher, and any DRM login thing
11. Try Asus Official / John's fork
It's going to take a while but then again you could also get it on the first try
