US Keyboard keeps changing to US International

Hi There,

I have a US keyboard (only) configured as an input device.

(macOS High Sierra - 10.13.3. MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports)

However, on regular occasions e.g. rebooting / starting up the keyboard annoyingly changes to U.S. International PC.

It's massively annoying as I use special characters in my password regularly on boot up have to go and select my US keyboard before I login in.

I have searched the form and found similar issues but no straightforward answer to fixing this problem.

Please help,

Thank You,

Aidan