@polagrj
I suggest you click the Help button in Canvas and report a problem.
Whenever new and strange situations like this one arise, we struggle to find potential ways, even if they are way out in left-field, that might explain it. They often require innovative thought and stretching the imagination. That might make them seem random, but they far from it.
There is a similar issue going on now where people are getting 0's for assignments that aren't yet due. That sounds similar enough that it influenced our suggestions for getting 100's. However, we had to try to turn it around into ways that it would give 100% instead of 0%. In Canvas, that could be due to people who have misconfigured their late policies. When late policies first came out, they were confusing and people frequently misunderstood.
Be aware that the answer that Canvas Support is giving to people in the other situation is -- at best -- partially incorrect. They are telling people the zeros that it can happen when you copy course content with a previous date into a course. That is correct. They then tell you to turn off the missing / late policies before you copy the content. If they mean the new blank course that you're copying into, that's just wrong because we have it off and it's the course copy that turns it on. If they mean the original course you're copying from, that may involve changing policies in a course that has grades in it.
It's possible that if you removed dates when you copied content, then it may not be an issue.
It's a bug that Canvas should fix, but it's not on their list of known issues. Instead, they try to put it on something that the user is doing wrong. It's happening too much this semester to seasoned users who know what to look for (it happened to both my wife and I teaching at different schools). That's the "at best" part of their solution. They put it out there as "this can happen", which is true, but it's happening even when that situation is not true. There are other situations where it occurs, so they are sending people down a rabbit hole as well.
I would encourage you to return here once you have the issue resolved and share the solution so we can be aware the next time someone asks about it.