In many languages, backslash-letter is a way to enter otherwise hard-to-type characters. In this case it's a "form feed". Examples:
\n — newline
\r — carriage return
\t — tab character
\b — backspace
To disable that, you either need to escape the backslash itself (backslash-backslash is a backslash)
'Normalized Distance in Chamber ($\\frac{x}{L}$)'
Or use "raw" strings where escape sequences are disabled:
r'Normalized Distance in Chamber ($\frac{x}{L}$)'
This is relevant to Python, not TeX.