It appears that
FAnimUpdateRateParameters::GetInterpolationAlpha is not returning a sensible value when running in TrailMode. Currently the only variable in the calculation is EvaluationRate which will usually be fixed. This means that the alpha value returned doesn't change as the number of skipped frames changes. It seems instead that we should be doing something like
return 1.f / (UpdateRate - SkippedEvalFrames);
This would match what we do in the budget allocator when we override the interpolation alpha.
See linked UDN for repro steps
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-192217 in the post.