well i did some more testing and i put that one h9 that has undulator on it in front of the amp instead of going in the loop..and it worked just fine.

i have a vht amp that has both send and return volume knobs for the effects loop—i put the pedal back where i usually have it and tried all different volume levels for the effects loop and still didnt work….so im guessing that the effects loop is either too loud and the algorithm is clipping?

is there a way to ajust the input level for just that algorithm?..because like i said …all the other ones work just fine.

Slightly confused, when running in the effect loop, is the problem that you don't hear any audio at all from Undulator when you turn the Intensity all the way up?  Or is it that the Undulator algorithm is clipping?  

Also, what is your H9 routing mode (Normal, Pre/Post, Wet/Dry), and are you running with Killdry on? 

I suggest trying some successive-simplest-as-possible setups to rule everything else out.  Start with just your guitar -> H9 running Undulator -> amp.  If that works as expected then move the H9 to the effects loop and try the simple setup of Guitar -> amp with H9 in the effects loop.