Based on my experience, the reason for this behaviour may just be bad 802.11n support, on 2.4Ghz wlan interfaces.
I have spent most of this weekend trying to understand the cause for this behaviour.
I'll spare you the headache. Here is a list of symptoms, what i tried to do, and the final solution.
List of symptoms:
1. While connecting using winbox to the ip/MAC, winbox is stuck at "Downloading descriptors"
2. When it connects, most of the time existing session windows are empty
3. When it's connected, opening a new terminal window returns nothing
4. Random winbox disconnects
5. High weird network latencys
6. Some WebPages (not Google) take a lot of time to open, and most of the time they don't open completely.
What i have tried to do:
1. RB reset
2. Tried several bridge/no bridge configurations for wlan1
3. Tried MAC Connection/IP Connection, all the same.
4. Tried clearing the "Appdata" folder and "clear cache" in Winbox loader, al lthe same.
5. Firmware upgrades to latest 6.45.8
6. Package upgrades to latest 6.45.8
7. Configuration reset, without default configuration.
Started from scratch and added only wlan1 in "default settings"
8. Tried exchanging the power supply, to another with 24V/1200ma, same thing, so its not the power supply.
9. I have 3 hap AC, updated all to the last 6.45.8, same problem in all of them, so it's not bad hardware/power supply.
10. Tried removing wlan chains, and leave just one chain, no help.
11. Used another computer to connect, same issue, so its not the computer.
12. Finally tried to disable 2.4Ghz "N" Band Modes. BINGO.
The final solution:
Don't use 802.11n on 2.4Ghz Mikrotik Interfaces.
Problem gone, low latency network and stable connection with 2Ghz-only-G.