How to reproduce:
1. Download and open attached "UIBugs" project
2. Load Scene "bug1" and enter Play Mode
3. Enter text at the end of the Input Field

Expected result: Console does not throw errors
Actual result: Console throws errors

Reproduced with: 2018.1.9f1, 2018.2.3f1, 2018.3.0a8

Note: The issue does not reproduce if the text is entered anywhere else, BUT the end of line of Input Field.
Disabling Horizontal Layout Group also fixes the issue.

Error:
Trying to add TextMeshPro - InputField Input Caret (TMPro.TMP_SelectionCaret) for graphic rebuild while we are already inside a graphic rebuild loop. This is not supported.
UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
UnityEngine.Logger:Log(LogType, Object)
UnityEngine.Debug:LogError(Object)
UnityEngine.UI.CanvasUpdateRegistry:InternalRegisterCanvasElementForGraphicRebuild(ICanvasElement) (at C:\buildslave\unity\build\Extensions\guisystem\UnityEngine.UI\UI\Core\CanvasUpdateRegistry.cs:229)
UnityEngine.UI.CanvasUpdateRegistry:RegisterCanvasElementForGraphicRebuild(ICanvasElement) (at C:\buildslave\unity\build\Extensions\guisystem\UnityEngine.UI\UI\Core\CanvasUpdateRegistry.cs:217)
UnityEngine.UI.Graphic:SetVerticesDirty() (at C:\buildslave\unity\build\Extensions\guisystem\UnityEngine.UI\UI\Core\Graphic.cs:104)
UnityEngine.UI.Graphic:OnRectTransformDimensionsChange() (at C:\buildslave\unity\build\Extensions\guisystem\UnityEngine.UI\UI\Core\Graphic.cs:131)
UnityEngine.RectTransform:set_sizeDelta_Injected(Vector2&)
UnityEngine.RectTransform:set_sizeDelta(Vector2)
TMPro.TMP_InputField:AssignPositioningIfNeeded() (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2743)
TMPro.TMP_InputField:AdjustRectTransformRelativeToViewport(Vector2, Single, Boolean) (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2996)
TMPro.TMP_InputField:GenerateCaret(VertexHelper, Vector2) (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2832)
TMPro.TMP_InputField:OnFillVBO(Mesh) (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2771)
TMPro.TMP_InputField:UpdateGeometry() (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2716)
TMPro.TMP_InputField:Rebuild(CanvasUpdate) (at C:\Users\UNITY-PC\AppData\Local\Unity\cache\packages\packages.unity.com\com.unity.textmeshpro@1.2.4\Scripts\Runtime\TMP_InputField.cs:2670)
UnityEngine.UI.CanvasUpdateRegistry:PerformUpdate() (at C:\buildslave\unity\build\Extensions\guisystem\UnityEngine.UI\UI\Core\CanvasUpdateRegistry.cs:150)
UnityEngine.Canvas:SendWillRenderCanvases() (at C:\buildslave\unity\build\Runtime\UI\ScriptBindings\UICanvas.bindings.cs:72)