In this situation, a FRuntimeFloatCurve UPROPERTY is stored in an Actor Component called CurveComponent. A Blueprint of MyActor (A subclass of AActor) is created and the CurveComponent is added to the Blueprint. A child of this Blueprint is created and then placed in the level. Editing the curve in the CurveComponent of any instances of this child blueprint results in any edits being lost when the map is reloaded, even if you save it.
This happened as far back as 4.15
To note, in addition to load, this will also occur after any edit to the Blueprint Actor instance in the Actor Details tab that results in a RerunConstructionScripts() call. For example, typing into the Transform's "X" loc and pressing ENTER.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-53466 in the post.