When trying to import or export a preflight library or a profile inside a library, the "file open" dialog does not open and instead throws a warning messagebox "Error in OS call SHGetFolderPath: -2147024829". See attached screenshot. This error of course hints to something in the underlying OS, but should be handled differently by Acrobat. For example, by instead opening a "file open" dialog in some default or safe directory instead.
I tried removing the registry key HKCU\Software\Adobe and its subkeys while Acrobat was closed. Then trying again, but it did not make any difference.
Probably not fully reproducable on every computer. Might be reproducable by importing a preflight profile, then removing the directory it was in, and trying to import a preflight profile again.
OS: Windows Server 2016, up to date as of 2021/01/21 (day of posting this issue).