KeepassX & YubiKey - cannot open database created with KeePass

In earlier versions of Ubuntu and KeePass I used to run KeePass with wine, but in the latest versions, the YubiKey is not detected in the wineenvironment ("error connecting to yubikey"). No problem, I thought: Let's use keepassx. Seems not that easy, though... I followed this comprehensive manual to install KeePassX with challenge response 2-factor support for linux (ubuntu/lubuntu). The repository ppa:hda-me/keepassx2-yubico for eoan is not yet available, but using bionic instead seems to work quite fine. At least on the first glance. Now I face two issues, and have no more idea how to solve them: 1. The challenge response option was available after the first startup, but the (definitively correct) password together with the YubiKey response did not work to open a KeePass database created under Windows. Therefore, my first question is: Is the encryption of KeePassX incompatible with that from KeePass, when using a challenge response as second factor? 2. Now, after some restarting and updating, the "challenge response" option is disabled (gray) and I lack any idea why. I am quite sure that keepassx was installed from the right repository. My second question: Any idea why the option is disabled and how to enable it? **Update:** When running keepassx from the console, the "challenge response" option is available. But not, when running KeePassX from the start menu. The correct combination of password and key response still results in "wrong key or file damaged". With the windows KeePass, the file can still be opened.