There are several steps you can take to identify the features which could result in errors during conversion.
%#codegen and coder.screener
Add the %#codegen pragma to the top of the MATLAB® file that is being converted to fixed point. Adding this directive instructs the MATLAB Code Analyzer to help you diagnose and fix violations that would result in errors during when you try to accelerate or instrument your code.
The coder.screener function takes your function as its input argument and warns you of anything in your code that is not supported for codegen. Codegen support is essential for minimum and maximum logging and data type proposals.
Consult the table of supported functions
See Language Support for a table of features supported for code generation and fixed-point conversion.
For information on what to do if a function is not supported for fixed-point conversion, see What to Do If a Function Is Not Supported for Fixed-Point Conversion.