Upgrading guppy basecaller on Oxford Nanopore Gridion via PPA

I am trying to update the guppy_basecaller (current version installed is 3.2.10+aabd4ec) on a ONT Gridion device. I am initially trying to update it via the nanopore PPA, as described here (requires login access to the nanopore community)

After I issued sudo apt update, I got a GPG error, saying that the public key was not found in the system.

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://europe.oxfordnanoportal.com/apt xenial-stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AD9D09AF2EBBA5A8
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://mirror.oxfordnanoportal.com/apt xenial-stable-gridion InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AD9D09AF2EBBA5A8
W: Failed to fetch https://mirror.oxfordnanoportal.com/apt/dists/xenial-stable-gridion/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AD9D09AF2EBBA5A8
W: Failed to fetch http://mirror.oxfordnanoportal.com/apt/dists/xenial-stable/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AD9D09AF2EBBA5A8
W: Some index files failed to download. They have been ignored, or old ones used instead

I came across a possible solution shown here, so I tried to add the key to the system with the following command:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys AD9D09AF2EBBA5A8

The terminal was busy for too long and, after some time I got an timeout error:

Executing: /tmp/tmp.EWnOg4cPJk/gpg.1.sh --keyserver
keyserver.ubuntu.com
--recv-keys
AD9D09AF2EBBA5A8
gpg: requesting key 2EBBA5A8 from hkp server keyserver.ubuntu.com
gpg: keyserver timed out
gpg: keyserver receive failed: keyserver error

I then came across this post where one potential solution was to change the port, so I issued:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys AD9D09AF2EBBA5A8

But then I got:

Executing: /tmp/tmp.sfqFuJpVb2/gpg.1.sh --keyserver
hkp://keyserver.ubuntu.com:80
--recv-keys
AD9D09AF2EBBA5A8
gpg: requesting key 2EBBA5A8 from hkp server keyserver.ubuntu.com
gpgkeys: key AD9D09AF2EBBA5A8 not found on keyserver
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0
gpg: keyserver communications error: key not found
gpg: keyserver communications error: bad public key
gpg: keyserver receive failed: bad public key

Has anyone managed to update the guppy_basecaller via PPA, as described in the nanopore community page?

An alternative would be to install via the .tar.gz file, though I am first trying to upgrade the current version from the PPA to avoid conflicts with the current installation.

sudo apt-get update
sudo apt-get install wget lsb-release
export PLATFORM=$(lsb_release -cs)
###
wget -O- https://mirror.oxfordnanoportal.com/apt/ont-repo.pub | sudo apt-key add -
###
echo "deb http://mirror.oxfordnanoportal.com/apt ${PLATFORM}-stable non-free" | sudo tee /etc/apt/sources.list.d/nanoporetech.sources.list
sudo apt-get update