Notes this issue does not occur on package updates 1.3.1 and above, but does occur on packages 1.2.4 and below. 

1. Create a new Unity project
2. Open window> Package Manager and then change from 'In Project' to 'Unity Registry'
3. Search or Find the collections package and then select 'Install'
4. In file explorer find the Project's 'Manifest.json' file and open it in a text editor or IDE
5. Change line "com.unity.collections": "2.1.4", from '2.1.4' to '1.2.4'
6. Switch back to the Editor and observe that the collections version number has changed
7. Select 'Update to 2.1.4'

Expected result: the package is updated and no errors are logged

Actual Result: 'UnsafeParallelHashSetExtensions.gen.cs' is thrown 243 times in the console and the player is unable to enter playmode or clear these errors unless the project is reopened.