It happened to me during minting that the browser blocked the JSON download and atm I have no idea how to recover the funds or if it is even possible. The recovery guide seems out of date.
During minting the JSON download is optional since there is no verification that the JSON download exists and yet the deposit address is generated and displayed anyway. For example the browser can block the download.
To ensure the user has the JSON downloaded correctly the minting process should require the upload of the JSON before the deposit address is generated and displayed.
Also it may be a good idea to show the blindingFactor and refundLockTime somewhere on the page once the deposit address is displayed.