What is access log actually showing

DoS attacks are blocked, period, but are logged.  You should not have "Disable Port Scan and DoS Protection" checked on the Advanced tab, on left Setup, WAN setup page. If you uncheck that box you lose that protection and they will get in. No need to block that IP Address as long as that box is unchecked, router never lets them in to even be blocked.

If they ARE legitimate and the router rejected a valid packet, TCP/IP is smart enough to regenerate the packet and it eventually gets to you. If logging in, you might notice it took longer.

Multiple DoS entry seconds apart are more than likely to be a real attack, although in some cases it is just someone trying ping you I think. If they are very fast, seconds apart, the router is supposed to shutdown entry for everything for a few minutes, but I have NEVER seen that happen.