The &cHash parameter of frontend plugins might have puzzled quite a few developers. That's why Kasper wrote an interesting article which explains how the &cHash mechanism works and what to avoid in order to make great, reliable plugins with TYPO3. A must read for every extension author!
Request parameters could not be validated (&cHash comparison failed)
The error is completely random, depending on browser and request.
As example, calling a page with chrome is going all done, calling with edge make the error.
A colleague of mine get the same page with Chrome or explorer and get always the error. Disabiliting cache on the page resolve the problem, but i didn’t want to do it