Assertion failed: Assertion failed on expression: 'outputVertexCount == sharedData.vertexCount'

I'm getting this on Unity 2017.1.0b5 after loading a particular scene, apparently it's not affecting the game.

 

I've got that error too in 2017.1.0b5 when I create a prefab (that contains a Canvas) as a child of an object with a Canvas component. I'm getting it in both editor (when I drag and drop the prefab) and play mode (when I instantiate the object).

 

Just installed the beta 2017.2.0.b2 because 5.6x still has the D3D11 crash bug (years now).
Opened up my project which has no issues and poof. spamming this same bug. So its still not fixed.

 

Bugs often occur in specific edge-cases only and reproducing is thus difficult.

If this issue is important to you, I recommend to submit a bug-report following the advice in this document. Using the bug-reporter seems to be an important step, because that makes sure the report is in their bug-tracking pipeline and has to be processed at some point. Using the forum is often used to add to an already submitted bug-report a little more attention.

It's from advantage to attach a project to the bug-report that Unity can use to reproduce the issue and test their fix against. The easier an issue can be reproduced by QA, the more likely it is to get forwarded to a developer, who might or might not work on a bug-fix for that at some point.

After you submitted the bug-report, you receive a confirmation email with a Case number. Unity often asks us to post the Case number in the forum thread, which allows them to find that bug-report if they look at your post.

Following these steps will increase the chance that Unity is looking at your issue tremendously.

 

I'll also add, that the same "observable bug" may have multiple root causes. So, we may have fixed one of the other root causes, but not yours. Without more information, we would be simply guessing at fixing what is exactly the issue you're running into. So, offering some repro to guarantee we can fix your root cause helps immensely.