I think you are trying to load the 5.2 plugins on a 6.0 system.
You will have to download the 6.0 versions using the Addon Manager. (Delete the gramps/gramps60/plugins folder first. You want to start fresh.)
Be certain to double-check the “Projects” tab to make certain that all of them have the 6.0 URLs. (There is another posting with a list of the collections outside of the Gramps-Project.)
For example, the following examples are curated 5.2 addon collection “projects” and, while the addons would download, they could not run on Gramps 6.x:
