Smart Punctuation Detected
It appears your device is changing the multiple consecutive hyphens (dashes) in your search to an en-dash character "–" or an em-dash character "—".
This is most commonly caused by iOS 11 on Apple devices. By default it has "smart" punctuation on, to do things like pretty curly quotes — and mess around with the hyphens you entered.
How many hyphens it takes for an en-dash or an em-dash seems to vary depending on the language settings on your device, so I can't reliably correct them back to the right number of hyphens.
Use a question mark rather than hyphen
One way round this bug/feature is to use a question mark "?" in place of each hyphen "-". There are other alternative characters available, see the examples page.
Turn off smart punctuation
Smart punctuation might cause you similar problems on other websites and apps, especially if you do any plain text editing, or coding. So you can turn it off.
On your iPhone or iPad, in Settings, tap General. Then, tap Keyboards, and toggle Smart Punctuation to off.