No subscription or cancleing anymore after Update

[fischhase]

Dear Gregor Agnes,

thanks for your great work. You ext is really nice, because it is so easy to use and as simple as it needs to be.

But now I have a problem: Ich had installed the version 6.1.0. At the Update to 6.1.1 there was an error:
PHP Warning: compact(): Undefined variable $alreadySubscribed in /usr/www/users/wieses/webseite/grassbirdhabitats.eu/typo3conf/ext/newsletter_subscribe/Classes/Controller/SubscribeController.php line 507

So I upgraded to Version 6.2. But now, by clicking on the link in the emails, I get always back to the subscribe oder unsubscribe form without any action. Did anything change, that I have to beware off?

At first, I will go back to version 6.1.0, but for a TYPO3 13 upgrade I will need some advice.
Thank you and regards
Martin