Openwrt doesnt respond hap ac2

Hello..
Unfortunately, my problem is with the internet connection and the device itself with all devices that are connected to the router.
The modem I connected to the router: TP Link Mr 600
Router: Hap ac 2
Flash memory used to increase storage space: 16 GB USB3
First of all, after installing Openwrt, I installed VPNV2 Ray using Passwall and configured and used it without any problems.
The problem that has occurred, which may take several minutes to several hours, is the disconnection of the Internet connection, but at the same time, it seems that the router itself does not respond. It may happen as soon as the router is turned on, and it may take 4-5 hours for it to happen.
It means that the ping from 192.168.1.1, which belongs to the tp-link mr600, is done without any problem, and also the ping of 192.168.2.1, which belongs to the openwrt router, is done without any problem.
But when the connection disconnection problem occurs, ping 8.8.8.8 requests timeout
Also, the interface does not respond and I cannot log in through 192.168.2.1
Also, SSH does not connect or is very slow to load
And I am sure that my internet connection has not been interrupted because I am directly connected to the internet modem with my phone and, for example, I am watching YouTube without interruption.
This problem may last for 10-15 minutes, and during this time, I cannot access any website, nor can I use an application, nor can I enter the router settings through the Luci interface.
In addition, if I disconnect from Wi-Fi at this time, I will not be able to connect to Wi-Fi again until the problem is resolved, and a message like: Baktash-2G is denied access will be displayed.
And unfortunately, I don't have the possibility to use it without VPN because I am in Iran and we need to use VPN for 99% of use
Meanwhile, I thought that the problem was with the flash drive and I changed it, but the problem was still there
At this time, I thought that the router was hanging and restarting, but then, after about 15 minutes, I saw that the router was showing 5 hours of uptime.

Hi

my first idea is that box is short on memory
out of memory condition
after 15 minutes, when SSH is restored, try to log to box and look at logread
maybe you will find some useful info

Thank you for your answer
I will definitely try this.
But I don't think it's a memory problem because I think it has a high RAM among all routers... 128 MB and the problem is, why does this happen? Because I didn't use anything but Passwall, and even if your short memory is correct and the memory is low. What happens when it suddenly gets fixed? Because I didn't reboot the router, I didn't change anything to make the memory go back to the previous state.

Hi

i am running rc4 on HAP AC2
6 SSID, 2 radios
no dhcp,no firewall, nothing, only DumbAP

              total        used        free      shared  buff/cache   available
Mem:         117168       62548       44784         352        9836       24952

it is already used half of MEM without stations connected
i have experienced lagging, slow response, ssh disconnects and similar symptoms with older 4/32 devices in OOM condition, similar as yours ...
but, maybe i am wrong :frowning:

Unfortunately, my problem has not been solved yet and I have no idea why this problem occurs
This time, this disconnection problem will be done faster and closer to each other
And during this time, when you want to enter the Luci interface, I will encounter a bad gateway message
Is this problem from OpenWRT? Is it from Pass Wall?
What should I do?