I, too, have ended up here trying to figure out why my canvas was showing this warning and would automatically reset itself.

Suggest adding the text, "Some UI features such as Text Mesh Pro utilize these channels."

The remark "Its up to the user to understand their use case..." only makes sense if the user KNOWS what is causing the channels to be added. In the case of Text Mesh Pro (a Unity supplied add on!) the user does not in fact know.

I just want add that I do not believe this Warning Message is enough in its current form.

I've dealt with this warning, cleared the tangent and normal flags, watched them come back when reloading the asset, only to get annoyed enough to finally look up why Unity wants to complain without allowing me to fix it.

I did not realize that this was all because of my reliance on TMP. It makes sense once you are given the reason, but I STRONGLY feel that it should be mentioned in the warning!

As others have pointed out, you guys integrated TMP years ago, why not make reference to the dependency or just flat out remove the warning if TMP components/package is preset?

There are so many times I run into these bizarre issues that are always listed "as intended". Clearly if your users are sufficiently confused as to the how or why behind something the engine is doing, your intentions may need to be made more apparent without us having to scour issue tracker, the forums, stack overflow, etc...

I use Unity 2019.3 with TextMesh Pro, had the same issue and just landed here. At least with this page, developers can understand what it's all about.

I still don't see the extra explanation message on TextMesh Pro suggested by Arthur-LvGameDev though, so I guess this issue has been marked Fixed but it has really been handled as By Design.

I understand why Unity wouldn't mention TextMesh Pro at the time it was a third-party plugin, but since it's now integrated you can expect more and more users use their components in their canvases.

Agree, the entire history of Unity has been like oh.. UI? .. well, let's make something really.. erh..

Why not a dedicated UI system, what's up with mixing it into the world and keep building on that really poor design over and again?

IMO the warning should be either removed entirely, or it should be in the documentation here and/or in the TMP documentation. Even better, make the warning say "One reason that you might need this is TMP" -- otherwise someone like myself ends up Googling to figure out why/if I need those channels, or if it's a bug when it resets each time after exiting Play Mode.

Morale of the story: It is a very poor UI/UX pattern as-is, and my mind would be blown if this was closed as "by design" -- UI/UX is critical to a PRODUCT, and something like this caused a 5-min search expedition for a veteran like myself; I'm sure less some developers have no idea what it does or file bug reports, etc.

IMO: Improve/fix the warning text to be more explicit about potential use-cases (or allow packages access to alter or disable the warning) + document the above -- and these are the minimums IMO (if it were my product, I'd do more for such a simple/small and quick UI/UX improvement)!