I’ll come back and clean this up, but for now:
Undocumented: It will use the default AWS profile – it will pull in your shared credientials, and use the default values if specified.
As per code, use AWS_PROFILE=<name> terraform import aws_db_instance.default <id> to import using a AWS profile that isn’t default.
ELB holds onto subnets that are to be destroyed. Combined with new subnet having the same CIDR, can’t create new subnet because CIDR is in use, can’t update ELB because new subnet isn’t created yet.