Troublesooting Tip: CLI Console frequent 'Connection Lost' after enabling web-svc-perf under log setting

When this problem occurs, the CLI console in the FortiOS web GUI may frequently close and display the message 'Connection Lost. Press Enter to start a new session.'.

The behavior happens when the Node.JS process unexpectedly restarts while web service logging is enabled.  To confirm if the issue matches this condition, review the crash log using the command 'diagnose debug crashlog read'.

Crash log example:

 diagnose debug crashlog read

.....

46: 2026-03-31 20:35:01 <02454> Node.JS restarted: (unhandled rejection)
47: 2026-03-31 20:35:01 <02454> TypeError: Cannot read properties of undefined (reading 'then')
48: 2026-03-31 20:35:01 <02454> at isPromise (/node-scripts/index.js:1:32204)
49: 2026-03-31 20:35:01 <02454> at n.value (/node-scripts/index.js:7:17114)
50: 2026-03-31 20:35:01 <02454> at CronSchedule.webRoutineCheck (/node-scripts/chunk-01e975858a15810f88
51: 2026-03-31 20:35:01 d9.js:4:464518)
52: 2026-03-31 20:35:01 <02454> at n.value (/node-scripts/index.js:7:17079)
53: 2026-03-31 20:35:01 <02454> at Cron.fn (/node-scripts/chunk-01e975858a15810f88d9.js:4:462428)
54: 2026-03-31 20:35:01 <02454> at Cron._trigger (/node-scripts/chunk-574b93e79e77ac579b5d.js:10:44202)
55: 2026-03-31 20:35:01 <02454> at Cron._checkTrigger (/node-scripts/chunk-574b93e79e77ac579b5d.js:10:4
56: 2026-03-31 20:35:01 4584)
57: 2026-03-31 20:35:01 <02454> at Timeout._onTimeout (/node-scripts/chunk-574b93e79e77ac579b5d.js:10:4
58: 2026-03-31 20:35:01 3777)
59: 2026-03-31 20:35:01 <02454> at listOnTimeout (node:internal/timers:581:17)
60: 2026-03-31 20:35:01 <02454> at process.processTimers (node:internal/timers:519:7)

These crash log entries appear each time the Node.JS process restarts, corresponding with CLI console disconnections and the 'Connection Lost' error.

Workaround:

Disable web service logging to prevent the issue:

config log setting
    unset web-svc-perf
end

Resolution:

A permanent fix is tentatively planned for FortiOS versions 7.4.13, 7.6.8, and 8.0.1, subject to change based on ongoing development and testing.