Where to get debian mirror status?

The following command fails right now (14:16 in EET timezone):

 docker run debian:buster apt-get update

The error being:

$ docker run debian:buster apt-get update
Get:2 http://deb.debian.org/debian buster InRelease [122 kB]
Get:1 http://security-cdn.debian.org/debian-security buster/updates InRelease [65.4 kB]
Get:3 http://deb.debian.org/debian buster-updates InRelease [49.3 kB]
Err:2 http://deb.debian.org/debian buster InRelease
  At least one invalid signature was encountered.
Err:3 http://deb.debian.org/debian buster-updates InRelease
  At least one invalid signature was encountered.
Err:1 http://security-cdn.debian.org/debian-security buster/updates InRelease
  At least one invalid signature was encountered.
Reading package lists...
W: GPG error: http://deb.debian.org/debian buster InRelease: At least one invalid signature was encountered.
E: The repository 'http://deb.debian.org/debian buster InRelease' is not signed.
W: GPG error: http://deb.debian.org/debian buster-updates InRelease: At least one invalid signature was encountered.
E: The repository 'http://deb.debian.org/debian buster-updates InRelease' is not signed.
W: GPG error: http://security-cdn.debian.org/debian-security buster/updates InRelease: At least one invalid signature was encountered.
E: The repository 'http://security.debian.org/debian-security buster/updates InRelease' is not signed.
$

Some answers on SO suggest this is an issue with Debian package repositories. If so, I assume this must be a known widespread issue right now.

Is there a place I could see the availability status of Debian packages repository? I found this, but it only contains mirrors.

As Debian themselves are saying:

The server deb.debian.org does not have packages itself, but the name has SRV records in DNS that let apt in stretch and later find places.

I see you are using it in a docker instance. Please make sure you have enough free space,etc. Looking it from a container point of view, you could try executing this command before running apt-get update

sudo apt clean