OverflowException occurs when package manager is docked in the editor and you start the project.
You can press clear and the message will disappear until the next time you start the project.

1. Create a new project.
2. Dock package manager in an editor window. (Open package manager with Window -> PackageManager)
3. Restart the project.

Expected Result: No errors are seen in the console.
Actual Result: "OverflowException: Value was either too large or too small for a character." error in console. (Full error message below.)

Reproducible in 2019.3.0a12.
Also tested in 2019.3.0a11, no error message.

OverflowException: Value was either too large or too small for a character.
System.Convert.ToChar (System.Int32 value) (at <ad04dee02e7e4a85a1299c7ee81c79f6>:0)
UnityEditor.Json+Parser.get_PeekChar () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Json+Parser.EatWhitespace () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Json+Parser.get_NextToken () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Json+Parser.ParseValue () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Json+Parser.Parse (System.String jsonString) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Json.Deserialize (System.String json) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.PackageManager.UI.AssetStore.AssetStoreClient+AssetStoreClientInternal.GetLocalPackages () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.PackageManager.UI.AssetStore.AssetStoreClient+AssetStoreClientInternal.List (System.Int32 offset, System.Int32 limit, System.String searchText, System.Boolean fetchDetails) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.PackageManager.UI.PageManager+PageManagerInternal.Refresh (UnityEditor.PackageManager.UI.RefreshOptions options) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.PackageManager.UI.PageManager+PageManagerInternal.OnUserLoginStateChange (System.Boolean loggedIn) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.PackageManager.UI.ApplicationUtil+ApplicationUtilInternal.OnStateChanged (UnityEditor.Connect.ConnectInfo state) (at <2c7108252b3f412abf2ec8c94fb7c234>:0)
UnityEditor.Connect.UnityConnect.OnStateChanged () (at <2c7108252b3f412abf2ec8c94fb7c234>:0)

License type: Pro