Proxy mcr.microsoft no longer works

When trying to pull Docker images through mcr.microsoft it will no longer work.
This is probably due to an upgrade with the HTTP client.

Steps to reproduce:
On 6.20:
Simply create a docker repository against https://mcr.microsoft.com and try to pull an image:

docker pull xx.xx.xx.xx:8081/docker-microsoft/dotnet/core/sdk:3.1.300-alpine3.11
3.1.300-alpine3.11: Pulling from docker-microsoft/dotnet/core/sdk
cbdbe7a5bc2a: Pull complete
80caa14a70db: Pulling fs layer
08a0d3029c8d: Pulling fs layer
76c18e0100a6: Waiting
f2d70053bcee: Waiting
b85289701b31: Waiting
ce7b9a608fb7: Waiting
error pulling image configuration: unknown blob

I then tried on earlier version - 6.16 and it worked:

docker pull xx.xx.xx.xx:8081/docker-microsoft/dotnet/core/sdk:3.1.300-alpine3.11
3.1.300-alpine3.11: Pulling from docker-microsoft/dotnet/core/sdk
cbdbe7a5bc2a: Pull complete
80caa14a70db: Pull complete
08a0d3029c8d: Pull complete
76c18e0100a6: Pull complete
f2d70053bcee: Pull complete
b85289701b31: Pull complete
ce7b9a608fb7: Pull complete
Digest: sha256:4062f048b316ead38ec15b0d3ff05a5c1986f801b38fcbe5f058f13e12820151
Status: Downloaded newer image for 10.1.21.94:8081/docker-microsoft/dotnet/core/sdk:3.1.300-alpine3.11
10.1.21.94:8081/docker-microsoft/dotnet/core/sdk:3.1.300-alpine3.11

Update: On 6.19.1 works as well.
So It's probably a regression due to the http client upgrade.