6.40.4 changelog:

*) address - show warning on IPv6 address when acquire from pool has failed;
*) arp - fixed invalid static ARP entries after reboot on interfaces without IP address;
*) crs1xx/2xx - fixed 1 Gbps forced mode for several SFP modules;
*) crs317 - added L2MTU support;
*) crs3xx - improved packet processing in slowpath;
*) defconf - fixed RouterOS default configuration (introduced in v6.40.3);
*) dhcp - fixed downgrade from RouterOS v6.41 or higher;
*) dhcpv6 client - added IAID check in reply;
*) dhcpv6-client - fixed IA check on solicit when "rapid-commit" is enabled;
*) dhcpv6-client - ignore unknown IA;
*) dhcpv6-client - require pool name to be unique;
*) e-mail - auto complete file name on "file" parameter (introduced in v6.40);
*) export - fixed wireless "ssid" and "supplicant-identity" compact export;
*) hotspot - fixed missing "/ip hotspot server profile" if invalid "dns-name" was specified;
*) hotspot - improved user statistics collection process;
*) ike1 - remove PH1 and PH2 when "mode-config" exchange fails;
*) ipsec - kill PH1 on "mode-config" address failure;
*) ipv6 - fixed IPv6 address request from pool;
*) lte - fixed modem initialization after reboot;
*) ntp-client - properly start NTP client after reboot if manual server IP is not configured;
*) rb931-2nd - fixed startup problems (requires additional reboot after upgrade);
*) routerboard - fixed "/system routerboard upgrade" for CRS212-8G-4S;
*) sfp - fixed OPTON module DDM information readings;
*) sfp - fixed temperature readings for various SFP modules;
*) snmp - fixed "/caps-man registration-table" uptime values;
*) snmp - fixed "/system license" parameters for CHR;
*) tile - improved reliability on MPLS package processing;
*) userman - fixed unresponsive RADIUS server (introduced in v6.40.3);
*) vlan - do not allow VLAN MTU to be higher than L2MTU;
*) webfig - improved reliability of login process;
*) wireless - added "etsi1" regulatory domain information;
*) wireless - improved WPA2 key exchange reliability;
*) wireless - updated "norway" regulatory domain information;

Download the new 'RouterOS 6.40.4' version here: https://www.mikrotik.com/download