Under URL part device/{device_id}/capture it is possible to run a discovery or polling on the fly and have the result be output to the browser.
Problem: When the corresponding PHP script includes/html/output/capture.inc.php sets a timeout for the symfony process, it uses snmp.exec_timeout (defaults to the reasonable 1200 seconds). Therefore essentially hundreds of SNMP commands need to run within this time. If you set 20 seconds instead, the run is basically doomed unless the device is really “fast” (or small). We have a slow Cisco switch which takes several minutes – not even 200s are enough.
My simple suggestion: Just use a dedicated timeout like capture.timeout, still defaulting to 1200 seconds.