Problem with password protected pages

There is a random problem with password protected pages on my website www.chasetrainingsolutions.co.uk. I have 2 pages that are protected with different passwords and clients sometimes are not able to access the page. This occurs randomly, as sometimes they can! This issue occurs on all web browsers, so is not isolated to one or two, i.e. Microsoft Edge, Chrome, Safari, etc. This is a frustrating issue :-(