During a recent release of DMS, Links to the details of Target Endpoints of Type S3 stopped working. The S3 buckets that are associated with the endpoints can be accessed via the S3 console and the Database migration tasks associated run without error. Also, all other endpoints work, even Source Endpoints of type S3. It is just the S3 Target endpoints that have this issue.
Here is the error message that is displayed when a link to the endpoint detail is clicked.

Endpoints

NOTE: After calling the cli command dms:describe-endpoints and comparing the output with the output from a test environment, there are no difference in the endpoint configurations.
However, the same error is now occurring in the test environment which has not been touched since January 26, at which point the error above was not present in both environments.
Below is the dsm:describe-endpoint output from a S3 Target Endpoint that is failing in the console.
{
"EndpointIdentifier": "aaaa-bbbbbbbb-data-dev-blue-dms-target-endpoint-bronze-s3-cccccccccccccc",
"EndpointType": "TARGET",
"EngineName": "s3",
"EngineDisplayName": "Amazon S3",
"ExtraConnectionAttributes": "bucketFolder=CCCCCCCCCCCCCCC;bucketName=aaaa-us-east-1-bbbbbbbb-blue-data-bronze-dev;CdcPath=cdc-files;compressionType=NONE;csvDelimiter=,;csvRowDelimiter=\\n;datePartitionEnabled=false;",
"Status": "active",
"EndpointArn": "arn:aws:dms:us-east-1:111111111111:endpoint:VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV",
"SslMode": "none",
"ServiceAccessRoleArn": "arn:aws:iam::111111111111:role/aaaa-bbbbbbbb-data-useast1-dev-blue-dms-s3-role",
"S3Settings": {
"ServiceAccessRoleArn": "arn:aws:iam::111111111111:role/aaaa-bbbbbbbb-data-useast1-dev-blue-dms-s3-role",
"CsvRowDelimiter": "\\n",
"CsvDelimiter": ",",
"BucketFolder": "CCCCCCCCCCCCCCC",
"BucketName": "aaaa-us-east-1-bbbbbbbb-blue-data-bronze-dev",
"CompressionType": "NONE",
"EnableStatistics": true,
"IncludeOpForFullLoad": false,
"CdcInsertsOnly": false,
"ParquetTimestampInMillisecond": false,
"CdcInsertsAndUpdates": false,
"DatePartitionEnabled": false,
"UseCsvNoSupValue": false,
"PreserveTransactions": true,
"CdcPath": "cdc-files",
"UseTaskStartTimeForFullLoadTimestamp": false,
"AddColumnName": true,
"CsvNullValue": "''",
"IgnoreHeaderRows": 1,
"MaxFileSize": 50000,
"Rfc4180": true,
"AddTrailingPaddingCharacter": false
}
}
This issue has now been resolved.