Spidertron Patrols 2.7.0 fails to load on Factorio 2.1.20/2.1.21:
Error while loading entity prototype "sp-spidertron-dock" (proxy-container): Value must be a list in property tree at ROOT.proxy-container.sp-spidertron-dock.circuit_connector
Cause: circuit_connector is now array[CircuitConnectorDefinition] (one entry per direction_count). prototypes/spidertron-dock.lua passes a single definition:
circuit_connector = circuit_connector_definitions["artillery-turret"],
Fix — wrap it in a list:
circuit_connector = {circuit_connector_definitions["artillery-turret"]},
Confirmed working locally with this one-line change.