In my understanding, Speed Loss and Minor Downtimes are two different things.
Speed Loss happens when you are producing slower than your standard rate.
Regarding Minor Downtimes, you can find the following statement "Minor downtime is not supported in the OEE implementation and all losses are treated as availability losses." in DM Help at https://help.sap.com/docs/sap-digital-manufacturing/execution/bbff7b7331014579968f7ae211d05b71.html?...
Hope it helps!