Looking into it, when the WF Matrix config is constructed afresh/manually you will get a total number of combinations estimate in the parameters info box. When loading a config to the WF Matrix stage the total number of combinations is always zero and never dynamically changes as you turn various parameterizations on and off. My guess is this has something to do with it.
Attached the WF Config that I always use (and works if setup like this manually) but always fails if loaded.