Here's my test:
-loaded 938 MF9:2 Undulator (this is the second Undulator preset)
-stored to user memory as #2
-reloaded from User memory
-press PARAMETER twice
-press ROUTING and select "series"
.press PARAMETER one more time
-press PROGRAM to select which algorithm to copy to the B block
-selected 161 Reverse Crystals & press LOAD FX B to load it
– no freezing occurs
BUT "This parameter cannot be modulated: Press any key to continue" appears…and shouldn't.
What algorithm did you choose to load in the FX B block?
I can't replicate the freezing here.