I turned off all of my plugins except for yours. I stopped getting any errors, but no image showed up for the Encyclopedia scene.
Viewing post in [CGMZ] Scene Backgrounds for RPG Maker MZ comments
The encyclopedia is a bit different because each category can have its own background image so it takes over management of showing the background from [CGMZ] Scene Backgrounds, you can set them up in the Category Backgrounds parameter under the Encyclopedia Scene Options category of parameters, you need to tell it your category id and your [CGMZ] Scene Backgrounds preset id, then it will use that preset for that category.
If you want to find out which plugin(s) are causing problems, you can try turning your other plugins on one by one until you start receiving the errors again, then you will know the last one your turned on is causing a conflict. It could be multiple if you are using a lot of plugins. If you can let me know which plugins cause a conflict I can maybe look into them, though if they are VisuStella they will be obfuscated which makes it difficult to see what is going on.