Troubleshooting Tip: FortiAP offline due to the 'Change state pending timer expired' error

[hgarara]

Description	This article describes how to resolve the error 'Change state pending timer expired' while FortiAP is showing offline.
Scope	FortiAP, FortiGate.
Solution	When FortiAP shows offline verify the reason for failure using the below command: TESTFGT1 # di wireless-controller wlac -c wtp -------------------------------WTP 1---------------------------- WTP vd : root, 0-FP12345678965432 MP00 uuid : 545678e8-c5yh-52tt-5454-a96034kj5n3 mgmt_vlanid : 0 region code : A valid refcnt : 3 own(1) wtpprof(1) ws(1) deleted(no) apcfg status : N/A,N/A cfg_ac=0.0.0.0:0 val_ac=0.0.0.0:0 cmds T 0 P 0 U 0 I 0 M 0 apcfg cmd details: plain_ctl : disabled image-dl(wtp,rst): yes,no admin : enable wtp-profile : cfg(FAP231G-default) override(disabled) oper(FAP231G-default) wtp-mode : normal wtp-wanlan-mode : wan-only cfg-apcfg-prof : oper-apcfg-pro : bonjour-profile : wtp-group : name : location : region-map : pos-x : 0 pos-y : 0 ble-major-id : 0 (wtp: 0, grp: 0, prof: 0) ble-minor-id : 0 (wtp: 0, prof: 0) led-blink : disabled led-state : enabled led-schedules : poe mode : full(auto) poe-mode-oper : full usb port : enabled(enabled from AC) usb port oper : enabled ext-info-enable : enabled ip-frag-prevent : TCP_MSS tun-mtu : 0,0 split-tunneling-acl-path : local split-tunneling-local-ap-subnet : disabled energy-efficient-ethernet : disabled active sw ver : FP231G-v7.4.5-build0734 local IPv4 addr : 10.11.1.1 board mac : aa:bb:cc:12:34 join_time : Mon July 8 7:12:49 2023 mesh-uplink : ethernet mesh hop count : 0 parent wtp id : connection state : Connected (0-10.11.1.1:5246) image download progress: 0 (upd-init,8099 hold 0 rst 0) last failure : 7 -- Change state pending timer expired last failure param: N/A last failure time: Mon July 8 7:07:11 2023 station info : 0/0 .... Based on the above example FortiAP stayed offline due to the default echo timer/max retransmit. Follow these steps: config wireless-controller global     set max-retransmit 3 <----- This is a default value - (Change the value to 25). end config wireless-controller timers     set echo-interval <1-255> <------ increase to 100. end The FortiAP came online: