Since the error is with the "split" function, which is not something you are explicitly calling in the function being compiled, there might be a shadowing issue occurring. To view all implementations of the "split" function in the MATLAB path, you can execute:
>> which -all split
to print out all the files called "split.m". By default in R2020b on Windows, the first one that shows up should be:
C:\Program Files\MATLAB\R2020b\toolbox\matlab\strfun\split.m
If this is not the first file that shows up, then the other implementation is shadowing the built-in "split" function, which is causing the error. Renaming or removing that other file will solve this error, but be aware that it may break the other program that is using that split function.
If the output of "which -all split" is also the same in R2018a, this is because there were changes made during the dependency analysis process in between the two releases that implicitly call the "split" function in MATLAB R2020b, but not MATLAB R2018a.
