Your log indicates that Content/models/animations/Running/Girlbase_run_backwards.uasset is hitting an assertion in UAnimSequence:PreSave(), observe the following section from the log:
The assert is saying that !DoesContainTransformCurves() || (RawAnimationData.Num()==0 || SourceRawAnimationData.Num() != 0) evaluates to false for the UAnimSequnce object associated with the GirlBase_run_backwards.uasset object. Looking at the code, this assertion is called by UAnimSquence::PreSave(). The assertion is telling us that Transform Curves exist without any source data.
Double check the asset to make sure it is properly configured. If you’re sure everything is properly configured, try force resaving this asset. If the problem persists, remove the asset from your project and try rebuilding.