This could be caused by the presence of invisible Unicode characters.
Many invisible characters that can appear as a space when printed, but there are also characters like the Zero-Width Non-breaking Space (ZWNBSP; Unicode char U+FEFF) that are completely invisible and don't take up space.
It can happen that such characters are read from data sources and can lead to unexpected behavior for example with string comparison.
Even when they are invisible, they can still be filtered out by the strrep function:
Identifying that such a character is present is probably the biggest challenge when such an issue is found or noticed. The strlength function accounts for such characters.
See the attached example that is using the mentioned ZWNBSP.
