Both Azure and AWS have limits to the amount of resources that can be created in each region, but it is more relevant for AWS, where the default values are usually lower.
The amount of the concurrent recovery activities is limited by AWS EC2 import service. The AWS import service is responsible for creating AMI from VMDK files during the process of a recovery. The AWS default of concurrent imports is 20 per region. Contact AWS support (for free) in order to increase this default limitation.