Error message when saving an article

Hello,

When I choose a category for an article that is not yet registered, I get the following message:
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Notice: Trying to get property 'id' of non-object in /home/clients/3a45f187b4ae9695253909db54f59351/sites/lerougegorge.site/plugins/content/route66seo/route66seo.php on line 54

Notice: Trying to get property 'catid' of non-object in /home/clients/3a45f187b4ae9695253909db54f59351/sites/lerougegorge.site/plugins/content/route66seo/route66seo.php on line 54

Notice: Trying to get property 'language' of non-object in /home/clients/3a45f187b4ae9695253909db54f59351/sites/lerougegorge.site/plugins/content/route66seo/route66seo.php on line 54

Notice: Trying to get property 'route66seo' of non-object in /home/clients/3a45f187b4ae9695253909db54f59351/sites/lerougegorge.site/plugins/content/route66seo/route66seo.php on line 57
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However, if I save the article before, I don't get this error message.

It's not a big deal, but it's just a little annoying.

What do you think is the source of the problem?

Thanks in advance.
Olivier