Attempts to install some apps (Thunderbird in these examples) from the AppCenter fail with:
Aborted due to failure (While trying to checkout 7898e3822e6f10310c8f2b6ae8aa630ed102eb1e3341c7e57e0aa9757987d2ea into /home/mg/.local/share/flatpak/runtime/org.freedesktop.Platform/x86_64/20.08/.7898e3822e6f10310c8f2b6ae8aa630ed102eb1e3341c7e57e0aa9757987d2ea-7UOQA1: Opening content object f5177de959293d7382c1995623c8ef3a389e90e48c801a2c4ef4d1ff74e1b0c3: Couldn't find file object 'f5177de959293d7382c1995623c8ef3a389e90e48c801a2c4ef4d1ff74e1b0c3')
There's a similar error when attempting to install from flathub.org:
While trying to checkout 7898e3822e6f10310c8f2b6ae8aa630ed102eb1e3341c7e57e0aa9757987d2ea into /home/mg/.local/share/flatpak/runtime/org.freedesktop.Platform/x86_64/20.08/.7898e3822e6f10310c8f2b6ae8aa630ed102eb1e3341c7e57e0aa9757987d2ea-4ERGA1: Opening content object f5177de959293d7382c1995623c8ef3a389e90e48c801a2c4ef4d1ff74e1b0c3: Couldn't find file object 'f5177de959293d7382c1995623c8ef3a389e90e48c801a2c4ef4d1ff74e1b0c3'
Krita also fails while Desktopius is successful. I'm left with installing (often old versions) from Synaptic.