WPMUDEV Dashboard update to v4.0.4 causes 504 Gateway Time-out

Dear Support,

I upgraded to WPMUDEV Dashboard v4.0.4 on a multisite installation and I now cannot access the admin section of the website. I am effectively locked out of the network.

Message: "Gateway Time-out The gateway did not receive a timely response from the upstream server or application."

I applied the same plugin update to a second multisite network and I get the exact same error.

I ensured the auto update feature was turned off, as advised, before installing the update.

Thanks in advance,
Will