It could be a variety of reasons, the most common being missed echos between the AP and the HiveManager.
The HiveManager and the APs have a call and response check-in system that allows them to confirm that each side of the connection is still responsive; these call and response packets are called echos. There is a specific time window within which an AP would need to respond to an echo to be considered still responsive. If the AP misses a certain number of echos back to back, it is considered disconnected until it responds again. If an AP is still connected to the internet and passing traffic while missing echos, it's likely due to latency on the network; the AP is unable to process the echo request quickly enough due to the amount of traffic it has to process before responding. To confirm that we are missing echo packets, we'd want to SSH in to an AP to enable CAPWAP debugs and then collect tech data.
CAPWAP debugs:
_debug capwap info
_debug capwap basic
_debug capwap stat
These will be erased if the AP reboots. You can also manually disable these at any time by adding "no" to the start of the command; for example "no _debug capwap info".
To get tech data, if you are using HiveManager Classic (myhive.aerohive.com):
Monitor> Select the check box next to the AP> Utilities> Get Tech Data.
To get tech data, if you are using HiveManager (formerly NG, cloud.aerohive.com):
Tools> Utilities> Get tech data> Check the box next to the device> Get tech data (blue button at the top of the page this time).
This guide reviews how to get tech data from the CLI of the AP in case that is easier:
https://thehivecommunity.aerohive.com/s/article/Collecting-Tech-Data-via-CLI
