We have simplified the agent setup as there was a lot of overlap and a lot of confusion for our users about which agent type to use. This meant some agent types were deprecated. It is likely that the agent you’ve used was one of those types. I’d recommend putting in a new agent of the default type and reconnecting the model & memory nodes.
Here’s the change for more info - feat(core): Make Tools Agent the default Agent type, deprecate other agent types by Cadiac · Pull Request #13459 · n8n-io/n8n · GitHub