Error "register_class(...): already registered as a subclass"

Hi,
I have some self made addons that used to work without error, and are still working fine because they are enabled and saved with the start up file. But when I disable, then reenable them, I get the following error message and it prevents me from enabling them again.
When googling it, I saw that’s a recurring error with API changes, but I couldn’t figure out what is wrong with my code… Any ideas?

Thanks.

The error:

The __init __.py:

The Displayer.py:
2

The addon_utils.py:
3

relaunch blender