The association between the wireless client and the Access Point (AP) can flap if there is Radio Frequency Interference (RFI) in the channel (cell) used by the AP and the wireless client.
RFI is the presence of unwanted interfering radio frequency signals from different sources which disrupt the original data signal from the AP and wireless clients. This results in intermittent connectivity issues between the AP and the wireless client and in some cases can lead to poor throughput, and low data rates.
You can use these methods to resolve this issue.
The best solution to eliminate the RFI problem is to identify the source or device which generates the unwanted RF signals and then remove that source. This ensures that there is no other RF device operating in the same cell (channel) as the WLAN devices. You can use a Spectrum Analyzer to detect the presence of RF activity in a channel. You can also use the Carrier Busy test option available on Cisco Aironet devices to test for the presence of RF activity. For more information on the Carrier Busy test, refer to Running the Carrier Busy Test
You can also try to use a different channel for the WLAN communication. For example, if unwanted RF signals disrupt one channel, (for example channel 11), you can configure the wireless bridge or the AP to use another channel, (for example channel 3), where there is no RFI.
Conduct a site survey. A site survey is used to determine the best placement and coverage (overlap) for your network's infrastructure devices. It is always advisable to perform a site survey before implementing any WLAN network to ensure high throughput and consistent performance. For more information on a site survey, refer to Performing a Site Survey.