Brand new hap-ac rb952ui-5ac2nd-us - tried many times buy on 
get failure to load rb.elf file.

pi@raspberrypi:~/Downloads $ sudo dnsmasq  -i  enxb827eb31e919 --dhcp-range=192.168.1.100,192.168.1.200 --dhcp-boot=/home/pi/Downloads/rb.elf --enable-tftp --tftp-root=/home/pi/Downloads/ -d -u pi -p0 -K --log-dhcp --bootp-dynamic
dnsmasq: started, version 2.76 DNS disabled
dnsmasq: compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC loop-detect inotify
dnsmasq-dhcp: DHCP, IP range 192.168.1.100 -- 192.168.1.200, lease time 1h
dnsmasq-tftp: TFTP root is /home/pi/Downloads/ 
dnsmasq-dhcp: 4277542130 available DHCP range: 192.168.1.100 -- 192.168.1.200
dnsmasq-dhcp: 4277542130 vendor class: Mips_boot
dnsmasq-dhcp: 4277542130 tags: bootp, enxb827eb31e919
dnsmasq-dhcp: 4277542130 BOOTP(enxb827eb31e919) 192.168.1.160 cc:2d:e0:fc:16:51 
dnsmasq-dhcp: 4277542130 bootfile name: /home/pi/Downloads/rb.elf
dnsmasq-dhcp: 4277542130 next server: 192.168.1.10
dnsmasq-dhcp: 4277542130 sent size:  4 option:  1 netmask  255.255.255.0
dnsmasq-dhcp: 4277542130 sent size:  4 option: 28 broadcast  192.168.1.255
dnsmasq-dhcp: 4277542130 sent size:  4 option:  3 router  192.168.1.10
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160
dnsmasq-tftp: failed sending /home/pi/Downloads/rb.elf to 192.168.1.160


folowing is release info for mikrotik hap ac
What's new in 6.43.4 (2018-Oct-17 06:37):

Changes in this release: 

*) bridge - do not learn untagged frames when filtering only tagged packets;
*) bridge - fixed possible memory leak when VLAN filtering is used;
*) bridge - improved packet handling when hardware offloading is being disabled;
*) bridge - properly forward unicast DHCP messages when using DHCP Snooping with hardware offloading;
*) crs328 - improved link status update on disabled SFP+ interface when using DAC;
*) crs3xx - fixed possible memory leak when disabling bridge interface;
*) crs3xx - properly read "eeprom" data after different module inserted in disabled interface;
*) dhcpv4-server - use client MAC address for dual stack queue when "client-id" is not received;
*) dhcpv6-server - fixed dynamic binding addition on solicit when IA_PD does not contain prefix (introduced in v6.43);
*) dhcpv6-server - recreate DHCPv6 server binding if it is no longer within prefix pool when rebinding/renewing; 
*) ipsec - allow multiple peers to the same address with different local-address (introduced in v6.43);
*) led - added "dark-mode" functionality for LHG and LDF series devices;
*) led - added "dark-mode" functionality for wsAP ac lite, RB951Ui-2nD, hAP and hAP ac lite devices;
*) led - fixed default LED configuration for SXT LTE kit devices;
*) led - fixed power LED turning on after reboot when "dark-mode" is used;
*) ntp - fixed possible NTP server stuck in "started" state;
*) romon - improved packet processing when MTU in path is lower than 1500;
*) routerboard - show "boot-os" option only on devices that have such feature;
*) traffic-flow - fixed post NAT port reporting;
*) w60g - added "frequency-list" setting;
*) w60g - added interface stats;
*) w60g - fixed interface LED status update on connection;
*) w60g - general stability and performance improvements;
*) w60g - improved stability for short distance links;
*) w60g - renamed "mcs" to "tx-mcs" and "phy-rate" to "tx-phy-rate";
 
What's new in 6.43.3 (2018-Oct-05 13:12):

(factory only release)
 
For a full changelog please visit https://mikrotik.com/download