Hi Matt Rittman,
This is certainly a frustrating time, so sorry to hear about your trouble.
I used a previous release of R18 and the 18.057 to test this. I can confirm that I get the same results. Weird, to say the least. I made a lot of tests to see if I can get closer to the problem, but no idea what happen, in terms of what could be done on interface level (vs code) to prevent this from happening.
However: Cineversity is not the place to submit bugs, this is a case for the support: (Don’t get me wrong, I’m happy to look into it, but things need to go their own way.)
https://www.maxon.net/en-us/support/how-can-we-help/
Nevertheless, I will of course submit the file below to the team.
The only way I get useable results is, to keyframe in a none R18.057 version the Bend Deformer, where the “Hammer” object had its keyframes, and perhaps on other positions as the information. Then switch the XPresso of and use the saved version in R18.057. Perhaps, not the best idea to continue with 18.057, if you ask me.
If you have no back up from your previous working version, please let the support know.
Below is a file, that is based on your findings. I have stored the values of the working version in plane vertices. So if opened in any working version the green values (starting after frame 320 in your case) should be the same as the red values.
Scene file:
https://www.amazon.com/clouddrive/share/IrTaa6LorfQ3kP8lmn3qhfkfech4lU4jHBmRZOvEXxy?ref_=cd_ph_share_link_copy
EDIT: It seems to happen when you have a different polarity (-/+) in the numbers than the Min/Max is set up, while a spline is present (an empty spline filed seems to behave neutral. Set the full range of input values as min/max and it should work. /edit
All the best