Sonoff S31 Lite Plug misbehaving since 2.3.3.140

Do you mean how many devices it is repeating for (assuming it can repeat)?

The simplest way would be to look at the output of the endpoint:

/hub/zigbee/getChildAndRouteInfo

The most informative way would be to use an Xbee3. You can put one together for about $30-40, with the added bonus that they form very good repeaters.