Strange URP package errors when updating from 2019.3.11f1 to 2019.3.14f1

Unity Engine
,
1

Opened a project I haven’t worked on for five months and got a barrage of errors. I have been googling desperately but can’t find any information or similar errors elsewhere. I have tried deleting the package.json, removing and reinstalling the package, all to no avail.

They mainly seem to revolve around this error:
The type or namespace name ‘NotKeyableAttribute’ does not exist in the namespace ‘UnityEngine.Animations’ (are you missing an assembly reference?)

Any ideas?

Library/PackageCache/com.unity.render-pipelines.universal@7.3.1/Runtime/2D/Light2D.cs(136,33): error CS0234: The type or namespace name 'NotKeyableAttribute' does not exist in the namespace 'UnityEngine.Animations' (are you missing an assembly reference?)
Library/PackageCache/com.unity.render-pipelines.universal@7.3.1/Runtime/2D/Light2D.cs(136,33): error CS0234: The type or namespace name 'NotKeyable' does not exist in the namespace 'UnityEngine.Animations' (are you missing an assembly reference?)
Library/PackageCache/com.unity.render-pipelines.universal@7.3.1/Runtime/2D/Light2DPoint.cs(20,33): error CS0234: The type or namespace name 'NotKeyableAttribute' does not exist in the namespace 'UnityEngine.Animations' (are you missing an assembly reference?)
Library/PackageCache/com.unity.render-pipelines.universal@7.3.1/Runtime/2D/Light2DPoint.cs(20,33): error CS0234: The type or namespace name 'NotKeyable' does not exist in the namespace 'UnityEngine.Animations' (are you missing an assembly reference?)
2

I exported the project as a package and imported into a new project, and that resolved it.