I wanted to make a manipulate where an ellips is moving if I move a point (p1 and p2). I calculate in a function the ellips and some points of it and return points in a list. The input values of the function are
the variables of the manipulate. I tested the function before, everything seems OK.
If I use the list of points (I hope they are dynamical) in the manipulate (the last in the notebook) the kernel crashes. I have a error message: An unknown box name (ToBoxes) was sent as the BoxForm for the expression. Check the format rules for the expression.
I added a notebook with comments. I hope someone will have the time to look. I tried already a couple of days.
Crash reproduced on "12.1.1 for Mac OS X x86 (64-bit) (June 19, 2020)". You should report this to Wolfram Support.
Works in the Wolfram Cloud version "12.1.2 for Linux x86 (64-bit) (September 9, 2020)" and cloud version "1.56 (September 30, 2020)"