The other day my wife and I became data gluttons, using up our monthly data allowance while we went grocery shopping, and I'm convinced it was iCloud's fault.

Over the course of one afternoon, we wiped our cell phone data, received numerous blaming text alerts from our wireless provider, and spent no small amount of time on the phone with tech support to troubleshoot. iCloud's fingerprints were all over our cell phone data. It's all over the weapon that beat us to the punch. But we figured out a way to hopefully prevent this from happening again.

Here's how the story of the missing data unfolded and what we are doing to prevent unwanted sequels.

My wife and I have very simple data needs and have been on the same shared 3GB data plan with Verizon for years and years. 3GB per month may not seem like much for two adults with iPhones to share, but we don't stream much and while out and about I think we've exceeded the 3GB limit maybe two or three times in the last few years, and two of those times were related to network tests we did for Tom's Guide.

So, with data usage hovering at less than 1GB, halfway through the billing cycle, my wife opened the Notes app on her Mac and wrote a grocery list and synced it to her iCloud account so she could refer to it later from her iPhone at the store, a world of pain she was about to unleash I had no idea. The list didn't immediately appear on my iPhone, but no problem.

I should mention here that my wife is in her home office and the Wi-Fi connection is fine, but sometimes erratic, because a feature on the iPhone called Wi-Fi Assist notices when the connection is weak and switches to cellular to help speed things up. This little sidebar will become very important in a little while.

Time passed and my wife went out to the grocery store. That's when I started getting text messages from Verizon. We were in danger of running out of data. We ran out of data. We had another 1GB data overage. Shortly after that there was another 1GB overage.

When you start getting a series of text messages like that within an hour, you know something is up. We logged onto the Verizon website and discovered that my wife's cell phone was sucking up data. We turned off my wife's cell phone connection and dove into Verizon to sort out what had happened.

A call with Verizon resulted in an adjustment to the plan to account for this sudden spike in data usage, but no explanation as to what was causing it. However, I am certain that iCloud sync is the cause for several reasons.

First, while I was looking through the Notes app on my wife's iPhone XR, the circular logo indicating that the notes were syncing between the device and the cloud was consistently there and rotating, suggesting that a major sync was underway. Then, after momentarily shutting off the cellular connection on my wife's phone, we now received a warning message from our Internet provider regarding data usage.

For over a year, we stayed home in preparation for a coronavirus outbreak, with two adults working from home and an elementary school student zooming in for a remote class. In all that time, we never received a single warning about data usage. And yet, on the day that iCloud seemed insistent on syncing everything my wife had stored on every device, our Internet usage spiked to the point that our ISP thought a warning was necessary. (Don't worry. We are not animals.)

What triggered the Great iCloud Sync of 21 years. I don't know if I am aware of this, but it probably has to do with a software update from Apple within the last week. My wife updated her iPhone to iOS 14.5 and her Apple Watch to watchOS 7.4 that week.The upgrade to watchOS 7.4 required her to temporarily unpair her watch from her phone and I wonder if it was because iCloud back and resync everything?

That's where the Wi-Fi assist setup comes to a head. My guess is that when my wife tried to sync the grocery list in the home office, Wi-Fi Assist detected a weak connection and decided to ease our burden by syncing all the iCloud data that had piled up via cellular. A review of Verizon's timeline for the start of the data surge confirms this hypothesis.

You won't be surprised to learn that we took our Wi-Fi Assist out to the back of the barn and put it there. At the very least, we disabled this feature.

If you are not sure if Wi-Fi Assist is enabled on your phone and you do a lot of syncing, you might be loath to turn it off. Here's how to do it.

1. Start "Settings" and select "Cell Phone.

2. Scroll all the way down the screen, past the list of individual apps on your phone, and find the Wi-Fi Assist button. Move the slider to Off.

If you are particularly paranoid about data, you can turn off cellular connectivity for individual apps that you don't want to use cellular data, but that may be overkill. if you turn off the iPhone's cellular switching feature, perhaps a surprising data surge could be prevented.

There is one more setting you can adjust, and you don't have to jump out of the "Cellular" section of "Settings. Tap "Cellular Data Options" at the top of the page. On the screen that follows, go to Low Data Mode and toggle that feature on.

When low data mode is enabled on the iPhone, automatic updates and other background activities (such as syncing) will be paused until you return to Wi-Fi.

Sadly, neither of these solutions has proven to be bulletproof. We spent a week or so going out and about all day with no data drain. But when my wife opened the Notes app for the first time, it at least confirmed that iCloud was the culprit.

So what do you do. We are considering reducing the number of notes stored in the cloud and doing a factory reset of the iPhone and iPad. I also went through the notes settings (Settings -> Notes -> Accounts -> iCloud) and tapped the fetch new data setting to change how often new data is pushed from the cloud to my wife's device. Still, don't be dissuaded from turning off Wi-Fi Assist and enabling low data mode. These two fixes may prevent future data plan disasters for you. And if we finally discover a surefire way to stop iCloud data problems, we'll update this post with the fixes.