I don’t have any experience with the SFS 1.0 but I do with 2.0 and I found it to be something of a finnicky beast.
Question for you - is there an LED on the SFS 1.0 that gives you the operation status? On the 2.0, there’s a Red LED that lights when there is no filament in the sensor and a Blue LED that flashes when the filament is going through it.
Do you have anything like this so you can see the status of the SFS?
Regardless, I did a bit of checking and found this discussing that might be useful to you:
It sounds like you have to add a pull up to your Raspberry Pi IO pin (10k should be fine).