BAS-files (Basic language) are treated by Bitbucket as binary, which caused the diffs not to show. This happens even the files are encoded in UTF-8
There are a number of possible reasons for a (seemingly) text-only file to be flagged as binary by our system. The most common of which involves characters which don't show up in most text editors.
If there is an example file exhibiting this behavior, feel free to reopen this issue so we can take a closer look.