Weird physics behavior when using AddForce and changing scale of Solver

[picross]

Hello,

I am currently working on a game where a blob is moving forward constantly and shrinking constantly. I learned that if you decrease the size of the solver, it decreases the size of the simulation space of the softbody and thus decreases the size of the softbody. I am using ObiActor.AddForce() with ForceMode.Force to propel the softbody.

It works great for a second or two, but then something weird happens. The softbody starts slowing way down, then it starts teleporting short distances forwards and backwards, and starts rolling backwards. The scale of the solver is always positive. 

Is this a limitation of the asset, or is there a way around this? I tried disabling the shrinking and setting the softbody to decreasing in size by a constant amount every time you press a button. When you press the button, the softbody teleports backwards a bit, then back forwards again and it massively decreases in speed.

Any ideas? Here's a gif of what happens in action: