Layout Managers causing TMPro Null Reference when filling vertex buffers

Pretty much the question, the full stack trace:
NullReferenceException: Object reference not set to an instance of an object TMPro.TMP_Text.FillCharacterVertexBuffers (System.Int32 i, System.Int32 index_X4) (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMP_Text.cs:5002) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:3594) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:2663) TMPro.TextMeshProUGUI.OnPreRenderCanvas () (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TMPro_UGUI_Private.cs:1656) TMPro.TextMeshProUGUI.Rebuild (UnityEngine.UI.CanvasUpdate update) (at Library/PackageCache/com.unity.textmeshpro@2.0.1/Scripts/Runtime/TextMeshProUGUI.cs:209) UnityEngine.UI.CanvasUpdateRegistry.PerformUpdate () (at C:/Program Files/Unity/Hub/Editor/2019.3.3f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/CanvasUpdateRegistry.cs:210) UnityEngine.UI.ScrollRect:LateUpdate() (at C:/Program Files/Unity/Hub/Editor/2019.3.3f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/ScrollRect.cs:805)
I have a UI canvas with layout elements and mixed horizontal and vertical layouts throughout, this error never occurred before I added them.