What does it fix excatly? Does it improve connection stability?
I have already created another thread concentrating on the status of the WiFi problems found in hAP ac^2 in the following thread.
Even applied the most recent RC (V6.42RC52), although the speed for 5G WiFi has already been increased from 20Mbps to 90Mbps, which is much below our expectations. We want the device to be capable to download file at a steady and stable rate of 500Mbps over at least an hour and not just few mini-seconds..
no
we couldn’t change LTE band from 3 to 7
in older versions
BGP4 MIB (RFC 4273) next please 
PPPoE Server not work into VLAN Interfaces
reverting back to 6.39.1 that works perfectly
tested with RB3011 and CCR1009
I use a vlan to deliver to each neighborhood or sector,
/interface bridge add name=LAN
/interface bridge port add bridge=LAN interface=ether5
/interface bridge port add bridge=LAN interface=ether6
/interface bridge port add bridge=LAN interface=ether7
/interface bridge port add bridge=LAN interface=ether8
/interface vlan add name=POP-CENTRO-SECTOR-LESTE interface=LAN use-service-tag=yes vlan-id=100
/ip pool add name=PPPoE-RES-1M ranges=172.16.11.1-172.16.11.126
/ppp profile add dns-server=172.31.255.2,1.1.1.2 local-address=1.1.1.2 name="1 MEGA" rate-limit="1M/1M" remote-address=PPPoE-RES-1M
/interface pppoe-server server add disabled=no interface=POP-CENTRO-SECTOR-LESTE default-profile="1 MEGA" service-name=BRAS1
Arriving in the neighborhood, i untag the vlan in the sectorial wlan like this (into my sectors SXT SA5).
/interface bridge add name=bridge1
/interface bridge port add bridge=bridge1 interface=wlan1
/interface bridge port add bridge=bridge1 interface=ether1
/interface wireless set [ find default-name=wlan1 ] vlan-id=100 vlan-mode=use-service-tag
the PPPoE server shows this looping log:
jan/01 21:04:16 pppoe,info PPPoE connection established from D4:6E:0E:BC:E2:FB
jan/01 21:04:16 pppoe,info PPPoE connection from D4:6E:0E:BC:E2:FB was already active - closing previous one
it is not a problem of the sector nor the wireless configuration this also happens by cable or fiber, untagging and dialing with any other brand that is not RouterOS not only works RouterOS dial PPPoE, can test, it is not a configuration problem, because everything worked perfectly in earlier versions,
I apologize for the long thread in the forum, but I’ve been posting a lot of time on the forums on Release Candidate until now, never solved.
reverting back to 6.39.1 that works perfectly
What kind of cases does it address?
The rbd52g hap ac2 wifi performance is really painful.
Mikrotik, please provide a statement to this.
In version 6.42rc52 on Hаp Ас^2 there are problems with Interface/interface list. Tools that use interface list do not work. Such as the MAC winbox server or parameter In. Interface list in firewall rules.
L2TP/IPSec wasn’t working for me in earlier RCs
I should have been more specific. Does it affect 6.41.3, or was introduced on this RC? Is it a problem with the wildcard no matching at all? Or matching too much? Or just matching incorrectly?
TIA
L2TP/IPsec works OK on 6.41.3 so it must have been introduced in the RC (or it is a problem I don’t notice…)
Yep, it was introduced in RC, just a few versions earlier. I noticed it on default configuration.
Ah, thanks. Good to know. 
Confirmation from MT in Mail RC55 will have fix for my LACP Bonding problem. Have a Nice week end and I hope for the soon Release of RC55. One wonder what more magical fixes will be included.
Let’s hope is doesn’t introduce new bugs after all that German beer… 
What’s new in 6.42rc56 (2018-Apr-09 08:18):
*) crs3xx - added initial “hw-offload” support for 802.3ad and “balance-xor” bonding;
*) dhcpv4-server - added “dns-none” option to “/ip dhcp-server network dns”;
*) dns - do not generate “Undo” messages on changes to dynamic servers;
*) ike2 - fixed framed IP address received from RADIUS server;
*) ippool6 - added pool name to “no more addresses left” error message;
*) ipv6 - fixed IPv6 behavior when slave leaves bridge;
*) ipv6 - update IPv6 DNS from RA only when it is changed;
*) led - added “Dark Mode” support for wAP 60G;
*) led - added w60g alignment trigger;
*) rb1100ahx4 - improved reliability on hardware encryption;
*) w60g - added “tx-power” setting (CLI only);
*) w60g - added RSSI information (CLI only);
*) w60g - added TX sector alignment information (CLI only);
*) winbox - fixed Neighbor Discovery and MAC Winbox (introduced in v6.42rc);
*) wireless - fixed RB911-5HnD low transmit power issue;
*) wireless - fixed wsAP wrong 5 GHz interface MAC address;
If you experience version related issues, then please send supout file from your router to support@mikrotik.com. File must be generated while router is not working as expected or after crash.
Note that release candidate versions are published strictly for testing purposes and should not be used on production routers.
This testing release (v6.42rc56) cannot resolve the poor WiFi performance issue in hAP ac^2. For details, please refer to the following link:
YH
In rc56 w60g multipoint is not working and there is no opportunity to generate support.rif. Its looks lock, reboot takes about 2 minutes to start.
hAP ac^2. When upgrading from rc52 to rc56, i get a bootloop again. Restored by netinstall.
hAP ac^2 upgraded correctly from rc52 to rc56 but wifi performance is still very poor - the same problem yhfung is talking about.