Searched through 15 years of questions on this. Nothing.
I found a solution. I needed to do the following:
(This assumes you’ve made a control rig to set morph curve values through the sequencer.)
Select your curve in the Rig Hierarchy (Interface left). Under Details / Value (interface right) of your control rig BP), set the minimum “(Min)” to: -1. (negative one) Done.
This issue has been floating for over a decade with no real answers. Daz morphs have a ton of in and out, highly useful morphs that will not work without this solution, as of summer '22.