Elastic Agent will not upgrade through fleet or locally

Hi,

We deployed the agent to a number of devices for testing. At the time the Elastic stack and Agents were on version 7.10.1 .

We have recently upgraded our stack to 7.12.0 and as you would expect the agents in fleet are requesting that they need an upgrade.

However if i issue the upgrade through fleet it sites for a while saying upgrading, then changes back to healthy but still retaining the old 7.10.1 version for the agent.

If i try and run the upgrade locally using;

C:\Program Files\Elastic\Agent> .\elastic-agent.exe upgrade 7.12.0

I get the following;

Failed trigger upgrade of daemon: cannot be upgraded; perform upgrading using Fleet

Is there any advice on troubleshooting this upgrade via fleet, or is it a known issue ?
Is my only course of action to fully remove the agent from the hosts and install the agent for 7.12.0 from fresh ?

Thanks in advance