AP本体やコントローラで以下のコマンドを実行すると、Reason Codeと詳細が表示されますので、ご確認ください。

service show wireless reference reason-codes

CODE DESCRIPTION
0 Success
1 Unspecified Reason
2 Previous authentication no longer valid
3 Deauth because sending STA is leaving IBSS or ESS
4 Disassoc due to inactivity
5 Disassoc because AP is unable to handle all currently assoc STA
6 Class 2 frame received from non-authenticated STA
7 Class 3 frame received from nonassociated STA
8 Disassoc because STA is leaving BSS
9 STA requesting association is not authentication with corresponding STA
10 Disassoc because info in the power capability elem is unacceptable
11 Disassoc because info in the supp channels elem is unacceptable
12 Reserved
13 Invalid IE
14 Message integrity code (MIC) Failure
15 4-way handshake timeout
16 group key handshake timeout
17 IE in 4-way handshake different from (re)association request/beacon
18 Invalid group cipher
19 Invalid pairwise cipher
20 Invalid AKMP
21 Unsupported RSN IE version
22 Invalid RSN IE capabilities
23 IEEE 802.1x authentication failed
24 cipher suite rejected because of the security policy
25-31 Reserved
32 Disassoc for unspecified, QoS-related reason
33 Disassoc because QoS AP lacks sufficient bandwidth for this Qos-STA
34 Disassoc because excessive frames need to be acked and have not been
35 Disassoc because STA is rtansmitting outside limits of its TXOP
36 Requested fmro peer STA as the STA is leaving the BSS (or resetting)
37 Requested from peer STA as it does not want to use the mechanism
38 Requested from peer STA as the STA received frames in a mechanism that requires setup
39 Requested from peer STA due to timeout
45 Peer STA does not support the requested cipher suite

※ 詳細の内容は以下のURLを参照ください。
https://support.zyxel.eu/hc/en-us/articles/360009469759-What-is-the-meaning-of-802-11-Deauthentication-Reason-Codes-

EXT0140