Controllerless Networks

Hi,
We have a problem with providing access to customers via Wi-Fi.
The problem: randomly (not dependent on time) the user lose access to the Internet (on DNS and IP).

Wi-Fi on device remains connected, other devices connected to the same AP was available from the problem device by ICMP and WEB and some was not.

Below screens according to the statistics of the user. As you can see from them device is connected but the Web interface does not show the speed.
The problem in mainly with Apple devices (iPhone, MacBook) are connected by 5Mhz.
The client does not be into the black list, and we don`t have configured the filtering rules.

We use Aruba IAP-205 access points with a virtual controller. Firmware version: 6.5.4.9_67129
The version of the device on which the problem was fixed iPhone SE version IOS 12.1.4
The following settings I changed, and they did not affect the appearance of the problem:
80Mhz support-enable/disable
Min transmit power-9/12
Max transmit power-Max/18
Broadcast filtering ARP/All
Clietn Match-enable/disable

The performance of the access point is not exceeded (Processor and memory are not loaded).
After reconnecting Wi-Fi on the device access restore.

And again, the problem mostly in (99% with Apple devices at 5Mhz).
I will provide all necessary configs if it is necessary.

Set "wide channels" to "none" (changes 40 mhz channels to 20).  You might not have enough 40mhz channels for good performance.

Set Arm min/max transmit power from 18/max to 12/18, instead (turns the power down on the 5ghz band to avoid cochannel interference).

Thanks for the help.
 I turned off 40Mhz and set the minimum power: 12 and maximum: 18.

But I did not quite understand:

..instead (turns the power down on the 5ghz band to avoid cochannel interference).

Do I need to turn off 5Mhz completely? But we have many users who connecting by 5Mhz.

Setting the minimum and maximum lower automatically turns down the power.