QuickLook Extension and App Groups on macOS

Hello, I am trying to use app groups to share preferences between an app and its QuickLook extension (both sandboxed), but I can't understand why it's not working.

For testing, I created an empty macOS app project and added a QuickLook Extension, then on both the targets' entitlement files I added the app group domain in the form "teamid.test". Last but not least, in the Info.plist file of the QL extension i added some UTIs to have the QL extension called when previewing.

In the QL extension's PreviewViewController.swift file I try to save a value like this:

func preparePreviewOfFile(at url: URL, completionHandler handler: @escaping (Error?) -> Void) {

        let defaults=UserDefaults(suiteName: "teamid.***")
        defaults?.set(1, forKey: "test")

        handler(nil)
    }

If I try to run the app and preview a file though, I get this message in the Console:

Couldn't write values for keys ( test ) in CFPrefsPlistSource<0x7fb63681cce0> (Domain: teamid.***, User: kCFPreferencesCurrentUser, ByHost: No, Container: (null), Contents Need Refresh: Yes): setting preferences outside an application's container requires user-preference-write or file-write-data sandbox access

And the value is not saved. The only way to make this work is to add a temporary exception in the extension target, like this:

<array>
	<string>/Library/Group Containers/teamid.***/</string>
</array>
</plist>

What bugs me is that if I try to save a value from the app instead, it works.

Are app groups not supported for QuickLook extensions?

Thank you, Michele