I used Walmart delivery for groceries a fair amount last year and didn't have a single issue. I used it maybe six times this year and there was an issue with the order five of those times. Several times it was delivered to the wrong address. The other times I was missing around half of my order. I was able to get refunds without any issue every time but the experience was so awful I canceled and haven't used it at all the second half of this year.
Your experience mirrors mine. My wife and I used Walmart+ for grocery deliveries basically every week for a year without any issues up until a couple of months ago. Suddenly, they started fucking up every single order, delivering things to the wrong address, missing items, or even claiming to have delivered an order that never arrived. After calling and complaining for the 10th time in a row, we gave up. We were so pissed off we even made a point of canceling the service, even though we get it for free as a credit card perk.