My search history showing up on another person's account

I have two Facebook accounts - my main one and a private one under a fake name that I use for things I don't want to be associated with my main account. Naturally, one of these things is searching for people and groups that I don't want showing up in my search history.

But it turns out the search history on my second account is showing up on my main account and so is my profile viewing history. Deleting my search history isn't enough, it still shoves the profiles I've viewed in my second account to the top of the suggestions in my main account. I should also point out that I only ever use my second account in incognito mode so none of it is in my browser's history.

What is the deal with this? I know Facebook doesn't give a damn about our privacy but this is beyond absurd.

Before anyone asks, no I have not accidentally been searching for these people/groups etc. on my main account. I double check each time that I am on my second account.

I can't really bring this up to Facebook itself because fake accounts go against the rules (but can you really blame me for wanting just a bit of privacy?) Plus, this can affect anyone who shares a computer with a family member. If you search for something in your account, your sibling, partner etc. will see your search history when they log in to their own account.