Reproduction steps:
1. Create and open a new Unity project
2. Open the manifest.json and add a scoped registry and a package
3. Focus back into Unity Editor

Expected result: Package is imported, console is clean
Actual result: After the package is imported, there are errors in console

Reproducible with: 2021.2.0a18, 2021.2.0b1
Not reproducible with: 2019.4.28f1, 2020.3.13f1, 2021.1.13f1

Note: Errors sometimes disappear after closing and reopening the Unity Editor. The alternative inconsistent reproduction steps would be to open the user's project and observe the console.

Errors:
An unhandled exception occurred:
Exception:
Method `Mono.Cecil.Mixin.CheckModule(Mono.Cecil.ModuleDefinition)' is inaccessible from method `Mono.Cecil.Pdb.PdbReaderProvider.GetSymbolReader(Mono.Cecil.ModuleDefinition,System.IO.Stream)'
Type:
System.MethodAccessException

An infinite import loop has been detected. The following Assets were imported multiple times, but no changes to them have been detected. Please check if any custom code is trying to import them: