We updated to Jenkins LTS 2.249.1 and also updated the EC2 plugin to 1.52.
After performing the update our existing EC2 key pair credentials were lost. It appears that the plugin is now supporting the Jenkins Credentials plugin.
When we attempted to set the credentials within the Configure Clouds UI, we'd see an error saying that this API required a POST. There was a button to provide the POST request. However, this did not actually save the credentials.
We have downgraded back to 1.50.3 to be able to continue to get EC2 slaves running again.