Fusion comp causing heartache...

I am trying to build a fusion comp that freezes 3 parts of a wobbly bad tilt:
The Head
The torso
the feet

I am putting 3 mediaIn nodes and have variously tried the timenode and using the MediaIn settings to create the freezes. The footage is Prores. I have numerous other Fusion comps that are stable and doing the right thing. This head/torso/feet thing crashes as soon as i adjust either the time node or the MediaIn footage adjuters

I tried removing the footage and changing a setting without the footage in and that crashed it too.

Edit:
3 mediaIn's - same footage each. (1920/1080 Prores @ 25)
Use media in footage selectors (In, Out, hold first/Hold Last) to select first frame.
view each in viewer. It is stable so far....
Connect to merges and merge over background to MediaOut _ Crash...relentless...

Edit more:
I lost too much hair so I made a tiff of each of the 3 parts and it worked as I anticipated.
Why it wouldn't work by freezing the Prores is a mystery that my hair is too precious for me to find an answer to. I suspect I need to understand the MediaIn tools better...

beta17.9
RTX 2080TI
128 gig ram
AMD 3950x
W10