Fill in the blanks - solution frozen for logged-in users

This issue arises only if the language of the exercise is set to "German" under "text overrides and translations":
1. A logged-in user who has already correctly completed a certain "Fill-in-the-blanks" exercise cannot repeat the same exercise because the solution will be displayed on revisiting it. This is awkward because it prevents intensive practice or testing alternative solutions that may have been defined by the designer of the exercise.
I have configured H5P exercises in such a way that they are accessible for any visitor of the website. Visitors not logged in are automatically encouraged to register / log in in order to earn points with GamiPress. If you do log in and visit a Fill-in-the-Blanks exerise that you already completed previously, you will see the completed solution. When you log out again, the solution disappears. Nothing of this kind occurs with other exercise types I am using.
The problem occurs also on devices and with browsers with which a solution of the particular H5P exercise has never been produced; consequently, the problem cannot be caused by cookies.
The problem ist perhaps difficult to replicate for a non-German speaker because you would have to produce a correct solution before you can replicate the problem. Therefore, I am uploading a screenshot of the solution of https://ondaz.de/von-welchem-verb-kommt-das-nomen/

2. WordPress 5.6.1; possibly caused by this version since I haven't noticed this problem before 5.6.1. However, I may have overlooked the problem.

3. Occurs both on desktop and mobile.

4. Tested on Firefox, Chrome, Opera and Edge. Always the same.

5. H5P 1.15.0. No update pending.

6. Site Health and Site Alert do not report any issues relevant to the problem.

10. The problem is not caused by GamiPress: It still occurs when I deactivate the trigger for a particular exercise in GamiPress.