Coming up for 3 years ago, my late husband's regiment held a drumhead service.
The Queen was the Colonel-in-Chief. We'd been told by the regiment that her previous visit to the regiment would be her last one.
Nevertheless, I got an invitation from regiment to attend to the service. Unusually, I was told that I had to confirm by x date and turn up on the day with two forms of ID.
On the day, I was surprised that no one was interested in my ID - just my ticket.
Got in. Found a place to stand. Was handed an Order of Service. It stated that it would take place in front of Her Majesty the Queen.
Podium party came out. Only the Duke of Kent.
The chaplain announced that the Queen had had to call off because of predicted bad weather disrupting her helicopter travel from Balmoral. In his autobiography, the D of K said the same (and commented on the irony that the weather had been fine).
My take on it is that anyone with a bit of common sense would have known that the Queen was too frail for the trip and that there should have been no expectation of the Queen's presence, particularly when we'd already been told that the her previous visit to the regiment was the final one.