Orders on LSE with Buy/Sell marked "Unknown"

I am a newcomer to LSE, which I use only for news and chat. I trade with Hargreaves Lansdown, whose per trade fee is only £5.95 if one does 20 or more a month (I do). Cheaper than LSE.
Yesterday I noticed four orders on the dealings page for Cap-XX Limited, all in the upper quantity range of normal for this share, which showed "Unknown" instead of "Buy" or "Sell". Then i saw each carried the note "Delayed notification of buy/sell". Is this a feature a trader can pay for as an add-on to mask their strategies? Or is it something altogether more innocent? From recent trading patterns of Cap-XX, I am pretty sure that are all Sells, but I would like to know about this feature anyway. Thanks for reading.

Hi DeffoTheLastSpin,

We calculate the trade type based on the trade price being higher or lower than the mid price at the time of the transaction. Sometimes this calculation does not work, or the price is the opposite side of the mid price. This means we are either unable to calculate what type of trade this is at all, or the calculation shows it as the wrong type of trade (a buy instead of a sell for example).

The above would explain why you sometimes see an Unknown trade. Delayed trades can happen from time to time, which can be due to various different reasons that we're not always told by the Stock Exchange.