Still getting memory crashes in NSOperationQueue (QOS: UNSPECIFIED) EXC_BAD_ACCESS 0x0000000000000000

[tikekar]

https://github.com/grpc/grpc-swift/issues/619 is still reproducible for us.

New Issue Checklist

• [ ] Updated grpc-swift to the latest version
• [ ] I read the Contribution Guidelines
• [ ] I searched for existing GitHub issues(especially, there are many resolved issues related to SSL)

Issue Description

Complete output when running grpc-swift, including the stack trace and command used

[INSERT OUTPUT HERE]

Environment

Key	Value
OS Version	x.x.x
Swift Version	x.x.x
Xcode Version	x.x.x
gRPC-Swift Version	x.x.x
gRPC-Swift Version	x.x.x
protoc Version	x.x.x
protoc-gen-swift Version	x.x.x
protoc-gen-swiftgrpc Version	x.x.x