Using custom resource names in CloudFormation can potentially cause resources' physical ids to exceed the allowed limit of 64 characters. Especially with nested stacks, as AWS::CloudFormation::Stack does not support custom names causing nested stacks to always be named automatically in the format <logical-id>-XXXXXXXXXXXX, with XXXXXXXXXXXX being a autogenerated identifier.
Below is an example of AWS::Lambda::Function within a nested CloudFormation stack.
Physical resource id is generated using the following format.
<root-stack-name>-XXXXXXXXXXXX-<lambda-function-name>
Quickly exceeds max length 64 characters.