I found the issue with codefling Ai assistant.
Go to this folder on your server
oxide/data/copypaste
Find the file named:
BGEasy_4.json
(or similar depending on exact naming)
Open it in a text editor.
Press CTRL+F and search for:
testridablehorse
You will find a line that looks something like:
"assets/rust.ai/nextai/testridablehorse.prefab",
Delete that entire line.
Save the file.
Reload the plugin:
rb.reloadconfig
or
rb.reload
After that, the base should load normally.