Unknown Box Name (ToBoxes) Error

I'm getting the following error in Mathematica

What is going on? How do I avoid such an error?

In order to roughly understand how I'm getting this error, here is a bit of context:

I'm using Manipulate to simulate some dynamics over a mesh. Given the mesh, one of the controls within Manipulate controls a horizontal stretch factor, which essentially transforms the mesh by scaling the first component of each vertex of the mesh by that factor. Everything works fine until a certain threshold factor value is used, from which I always get this error.

I'm afraid the code is too big to paste here, and I wasn't able to recreate the error in a simpler scenario. I suspect it might have to do with the notebook margins, since it seems that, once over a certain factor, the output panel would go beyond the normal width of my notebook, but I'm not sure.

Any ideas?

• Could you take it aside, delete part by part till you can't reproduce it and then come back with an example we can investigate? – Kuba Mar 27 '20 at 21:21
• @Kuba, yes, I believe that might be the best way to go about this. I will try to do that. I was just trying to understand the nature of the error. For example, what are these ToBoxes and BoxForm expressions? – sam wolfe Mar 28 '20 at 0:53