Our family has had 3 deliveries of Christmas food over the past few days.
first one: 3 sensible subs, 2 more missing items, none of the key items missing
second one: 1 sensible sub, 2 more items missing, no key items missing
third one (very big order): 4 sensible subs, 3 more items missing, no key items missing
All Ocado. Not bad at all given the supply chain issues that currently exist, and the sizes of the orders lrelative to number of missing/subbed items. We always put a bit of slack in our orders and then make up other meals or put in the freezer for later, so that missing items aren't the end of the world, as far as possible. I've had a few weird and wonderful subs over the years, a swapped non-food bag once, and a few accidentally-missing items, but I could count them on one hand. All refunded without question, of course.
I really can't be bothered to run around the shops as well as having a supermarket delivery if at all possible so for the most-part we cook with what's there. 15 items missing including a turkey etc. would piss me right off though. Which is why I only use Ocado, personally, as I've had good results with them before and during the pandemic, and not so good with a couple of other supermarkets.
I really do feel for everyone who is having trouble with their deliveries and getting slots at the moment, and consider myself fortunate to live in an area served by Ocado and be able to afford it. And near lots of supermarkets if I should happen to decide to go into one after all. I've been in very different positions in the past.