When testing a 150spm resource to science block with one slave module, I received the following error:
The mod Factory Modules (0.6.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factory_modules::on_tick (ID 0)
factory_modules/control/handlers/on_tick.lua:87: attempt to index local 'port' (a nil value)
stack traceback:
factory_modules/control/handlers/on_tick.lua:87: in function 'process_secondary_module_operations'
factory_modules/control/handlers/on_tick.lua:167: in function 'update_secondary_module'
factory_modules/control/handlers/on_tick.lua:211: in function <factory_modules/control/handlers/on_tick.lua:173>

Edit: I've gotten this error multiple times now.