Unable to deploy - SSH problem?

Hi all, hoping someone can help me with this as it's slowly melting my brain.

We use AWS and manage that through Forge to run a couple of applications. Two of which are the production and staging versions of our main application. To date, deploying new updates hasn't been an issue but yesterday, without any changes to the server (other than setting PHP 8.3 as Sites Default), I was unable to run any commands through the Forge interface nor was I able to deploy as any attempt failed with the following error:

Server Alert Description

Something went wrong when we tried to execute an action on your server. Sometimes this means we couldn't SSH into the server, or something may have gone wrong while executing a command.

Having SSH Problems?

Please make sure that the following SSH key is placed in both the /home/forge/.ssh/authorized_keys file and the /root/.ssh/authorized_keys file on your server.

[public key]

This has never happened before so I was a bit baffled so using the AWS console, I opened both files and the key appeared to be in there correctly. I also verified the permissions for the Forge account to ensure it had access and ownership.

To further add to the confusion, I'm also unable to SFTP in via FileZilla. Any attempt to do so presents me with the following level 3 debug (last few lines)

Trace:	Sent public key signature
Trace:	Access granted
Trace:	Opening main session channel
Trace:	Remote debug message: /home/forge/.ssh/authorized_keys:29: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
Trace:	Remote debug message: /home/forge/.ssh/authorized_keys:29: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
Trace:	Opened main channel
Trace:	Started a shell/command
Status:	Connected to 18.132.210.113
Error:	Fatal: unable to initialise SFTP on server: could not connect

So when trying to SFTP it appears to be accepting my key but not allowing me to connect and it seems possible that these two issues are related.

Weirdly, the aforementioned staging server is almost a mirror of this one and everything is working fine, just like this one was until recently.

Any help would be greatly appreciated, cheers.