Steps to Reproduce

1. On a Windows 10 machine, two local user accounts exist with separate KeePassXC databases.
2. User A signs in to Windows, opens its KeePassXC database and successfully uses the keepassxc-browser extension.
3. User B signs in to Windows (switching away from User A without signing out that Windows account) and opens its KeePassXC database and tries to use the keepassxc-browser extension.

Expected Behavior

The keepassxc-browser extension works at this point for User B (it is able to retrieve and populate usernames and passwords).

Current Behavior

The following error message appears:
Message encryption failed. Is KeePassXC running?
And after clicking reload, it says:
Key exchange was not successful.

Possible Solution

Note that User B works correctly if it is the first user account to sign in; there is not a problem with settings that normally prevents the connection when only that user account is signed in. I suspect there is some kind of communication port/channel that assumes only a single user account per machine.

Note that things worked much better on the most recent we had installed before 2.6.0.

Debug info

KeePassXC - 2.6.1 (also repro'd with 2.6.0)
KeePassXC-Browser - 1.7.0
Operating system: Win32
Browser: Chrome/Chromium 85.0.4183.83