This is the normal situation of our new AP:

# INTERFACE RADIO-NAME MAC-ADDRESS AP SIGNAL-STRENGTH TX-RATE UPTIME
0 wlan1 000C42313C3F 00:0C:42:31:3C:3F no -66dBm@6Mbps 54Mbps 2h1m18s
1 wlan1 000B6B4E2C7C 00:0B:6B:4E:2C:7C no -64dBm@6Mbps 54Mbps 47m35s
2 wlan1 000C42313C3C 00:0C:42:31:3C:3C no -77dBm@6Mbps 36Mbps 36m12s
3 wlan1 000C42317A11 00:0C:42:31:7A:11 no -65dBm@6Mbps 54Mbps 33m52s
4 wlan1 000C422CFF7F 00:0C:42:2C:FF:7F no -72dBm@6Mbps 54Mbps 24m53s

and 3 hours before from terminal console (I am sorry for incomplete output):

# INTERFACE RADIO-NAME MAC-ADDRESS AP SIGNAL... TX-RATE
0 wlan1 000B6B4E2C7C 00:0B:6B:4E:2C:7C no -64dBm... 54Mbps
1 wlan1 000C42317A11 00:0C:42:31:7A:11 no -71dBm... 48Mbps
2 wlan1 000C42313C3F 00:0C:42:31:3C:3F no -70dBm... 48Mbps
3 wlan1 000C422CFF7F 00:0C:42:2C:FF:7F no -87dBm... 24Mbps
4 wlan1 000C42313C3C 00:0C:42:31:3C:3C no -85dBm... 24Mbps

and their self-logs

16:58:55 wireless,info 00:0C:42:31:3C:3C@wlan1: disconnected, extensive data loss
16:58:57 wireless,info 00:0C:42:31:3C:3C@wlan1: connected
16:58:58 wireless,info 00:0C:42:31:7A:11@wlan1: disconnected, extensive data loss
16:58:59 wireless,info 00:0C:42:31:7A:11@wlan1: connected
16:59:25 wireless,info 00:0C:42:31:3C:3C@wlan1: disconnected, extensive data loss
16:59:38 wireless,info 00:0C:42:2C:FF:7F@wlan1: disconnected, extensive data loss
16:59:40 wireless,info 00:0C:42:2C:FF:7F@wlan1: connected
16:59:51 wireless,info 00:0C:42:31:3C:3C@wlan1: connected
17:00:21 wireless,info 00:0C:42:2C:FF:7F@wlan1: disconnected, extensive data loss
17:00:25 wireless,info 00:0C:42:2C:FF:7F@wlan1: connected
17:01:43 wireless,info 00:0C:42:31:7A:11@wlan1: disconnected, extensive data loss
17:01:44 wireless,info 00:0C:42:31:7A:11@wlan1: connected
17:02:06 wireless,info 00:0C:42:31:7A:11@wlan1: disconnected, extensive data loss
17:02:11 wireless,info 00:0C:42:31:7A:11@wlan1: connected
17:11:09 wireless,info 00:0C:42:2C:FF:7F@wlan1: disconnected, extensive data loss

AP version: "3.10" cpu: "MIPS 24K V7.4" cpu-frequency: 680MHz architecture-name: "mipsbe" board-name: "RB411"

We have changed for three times the hardware, configuration, send mail to mikrotik (without response) ecc.. but problem persists........
Replacing the new AP with an older model and the problem disappears!!!!!!!!!!!!!!!!!!!!!!!!!!!

Just for stay in theme same AP model on different locations (at tens of kilometers away) .....
# INTERFACE RADIO-NAME MAC-ADDRESS AP SIGNAL-STRENGTH TX-RATE UPTIME
0 wlan1 000C422CC89E 00:0C:42:2C:C8:9E no -81dBm@6Mbps 6Mbps 6d6h15m35s
1 wlan1 000C42317A18 00:0C:42:31:7A:18 no -80dBm@6Mbps 6Mbps 6d6h15m35s
2 wlan1 000C42317A07 00:0C:42:31:7A:07 no -77dBm@6Mbps 6Mbps 6d6h10m15s
3 wlan1 000C42317A10 00:0C:42:31:7A:10 no -80dBm@6Mbps 6Mbps 4d6h34m51s
4 wlan1 000C421BEE84 00:0C:42:1B:EE:84 no -88dBm@6Mbps 6Mbps 1d21h19m3s
5 wlan1 000C420C765F 00:0C:42:0C:76:5F no -87dBm@6Mbps 6Mbps 6h59m54s

and same logs....
jul/18 18:28:24 wireless,info 00:0C:42:0C:76:5F@wlan1: connected
jul/19 01:11:29 wireless,info 00:0C:42:0C:76:5F@wlan1: disconnected, extensive data loss
jul/19 08:22:50 wireless,info 00:0C:42:0C:76:80@wlan1: connected
jul/19 11:49:59 wireless,info 00:0C:42:0C:76:80@wlan1: disconnected, extensive data loss
jul/19 11:50:08 wireless,info wlan1: data from unknown device 00:0C:42:0C:76:80, sent deauth
jul/19 12:56:29 wireless,info 00:0C:42:0C:76:5F@wlan1: connected
jul/19 23:28:15 wireless,info 00:0C:42:0C:76:5F@wlan1: disconnected, extensive data loss
jul/19 23:34:44 wireless,info 00:0C:42:05:A0:7E@wlan1: connected
jul/20 01:18:44 wireless,info 00:0C:42:31:7A:16@wlan1: disconnected, extensive data loss
jul/20 02:07:51 wireless,info 00:0C:42:0C:76:80@wlan1: connected
jul/20 09:26:20 wireless,info 00:0C:42:31:7A:16@wlan1: connected
jul/20 09:42:51 wireless,info 00:0C:42:0C:76:80@wlan1: disconnected, extensive data loss
jul/20 10:21:39 wireless,info 00:0C:42:05:A0:7E@wlan1: disconnected, extensive data loss
jul/20 11:37:39 wireless,info 00:0C:42:31:7A:10@wlan1: disconnected, extensive data loss
jul/20 11:43:35 wireless,info 00:0C:42:31:7A:10@wlan1: connected
jul/20 12:28:49 wireless,info 00:0C:42:31:7A:16@wlan1: disconnected, extensive data loss
jul/20 16:34:31 wireless,info 00:0C:42:0C:76:5F@wlan1: connected
jul/20 23:42:32 wireless,info 00:0C:42:0C:76:5F@wlan1: disconnected, extensive data loss
jul/21 12:27:53 wireless,info 00:0C:42:0C:76:5F@wlan1: connected
jul/21 18:13:15 wireless,info 00:0C:42:0C:76:80@wlan1: connected
jul/21 20:07:26 wireless,info 00:0C:42:1B:EE:84@wlan1: connected
jul/21 21:46:57 wireless,info 00:0C:42:0C:76:80@wlan1: disconnected, extensive data loss
jul/21 21:55:22 wireless,info 00:0C:42:1B:EE:84@wlan1: disconnected, extensive data loss
jul/21 23:05:22 wireless,info 00:0C:42:0C:76:5F@wlan1: disconnected, extensive data loss
jul/22 09:39:00 wireless,info 00:0C:42:0C:76:5F@wlan1: connected
jul/22 18:47:36 wireless,info 00:0C:42:0C:76:5F@wlan1: disconnected, extensive data loss

..................We have dozens of new configured AP devices with the same problem

personally I think Mikrotik is underestimating the problem because so far there has been an appropriate response to the solution of the problem.
From three over three years we are exclusively using Mikrotik equipment to serve our customers and so far we have always found good, but honestly this time we feel deeply disappointed ......
As soon as possible if they do not find a solution to the problem, unfortunately (and I am sorry to say) as provider we are forced us to find a more radical....

Sorry it outburst but when it bears a worrying situation with no answer sooner or later it bursts ........

Bye

what do you mean with replacing with older model - what version is using the older model?
Make sure that you have the same wireless configuration in both: old and new model.
Try to increase the hw-retries value.

Hi staff
This is the old model:
routerboard: yes
model: "532"
serial-number: "111301D4C5E8"
current-firmware: "2.5"
upgrade-firmware: "2.12"
I don't have configuration because we have used it only for test, but
signals level appears more more stable and with a very minor number of
extensive data loss.
In the new model
routerboard: yes
model: "411AH"
serial-number: "1A7201CF8974"
current-firmware: "2.16"
upgrade-firmware: "2.20"
with the follow system resource print
uptime: 9h48m3s
version: "3.27"
free-memory: 51440kB
total-memory: 62440kB
cpu: "MIPS 24K V7.4"
cpu-count: 1
cpu-frequency: 680MHz
cpu-load: 9
free-hdd-space: 28088kB
total-hdd-space: 61440kB
write-sect-since-reboot: 1479
write-sect-total: 103357
bad-blocks: 0
architecture-name: "mipsbe"
board-name: "RB411AH"
we have upgraded version at 3.27, and it work only with 5 cpe, while
work fine with over twenty cpe end very small number of
extension data loss however justifiable.....
Can we have a method for debugging this problem?

Many thanks staff for your response.