What tessellation shader are you using on ios that is currently working? Can you share it with us for further investigation, together with the ASE shader? You can do so via firstname.lastname@example.org if you'd rather share it privately.
The tessellation technique used in ASE is the same as Unity's so, if Unity's tessellation shaders are working in ios, so should ASE.
The sample I've sent is a Unity Standard shader and, since we use Unity's Tessellation on ASE, if it doesn't work it means that there is an issue on Unity side regarding support on iOS.
If this sample works, it means that there is in fact an issue on our side, and we will proceed to investigate it.
On a side note, I did notice that they mention at the end of the manual page I've shared that they've added support for Tessellation for Metal added in 2018.1, but this might not guarantee that it works on all devices.
It seems that Unity's tessellation technique still has some issues, unfortunately there's nothing that we can do on our side in regards to this. As such, I'd suggest that you get in touch with Unity to report the issue you're having while also providing details such as Unity version and target device.
We'll also be keeping an eye out for any possible fixes on Unity's side regarding tessellation on iOS/Metal issues.
Apologies for the inconvenience, please don't hesitate to get back in touch if you come across any other issues.
I had a similar issue. In unity 2018.2.14. I am using windows to build for Xcode on my mac. I have everything updated to 12.1 iOS, latest xCode.
So in Unity I have to set my Graphic Emulation to none to see the Tessellation in editor. I use Amplify shader and I have to also check Direct X 11 as a target in Amplify shader to see the effect in editor. But I still had issues when I went to build to my iPad (2018). Amplify tessellation materials would not show up. But Unity's Standard Tessellation shaders did work when I ran a build. So I decided to duplicate my Amplify shader and edit it in Visual Studio to match closer to the unity tessellation naming and convention. I also removed the ASE elements (so it won't open in the Amplify Shader Editor) And that worked. I now have my custom built shader from amplify working, but have lost the ability to edit it visually. I have not dived deeper yet to find the exact change I need to make, maybe it's something I am missing in the Shader Editor Properties.
So I can confirm that in a build the Unity Standard Tessellation shaders are Working. Amplify shader has some issues that can be addressed by matching closely to the Unity Standard shaders. Finally It appears that the Graphic Emulation Metal in the Unity Editor is not working with Tessellation so use None.
We've just tested our Tessellation sample, together with the Unity's Tessellation samples provided here, in the latest version of MacOS, and it seems that out sample is working in editor and also in a build ( Metal ), while Unity's own snippets are giving errors, so we're not entirely sure on what could be causing the reported issue.
In order for us to help you any further and to successfully debug any issues you might have with the ASE, we'll need a sample project with the issue present, so that we can proceed to investigate it using the same data as you.