Bluetooth Keyboard MUST Re-Pair at Startup

I have a MacPro 1,1 with the old school thick Bluetooth keyboard (As shown in the picture attached to this post).

What I'm about to describe has happened since I bought it brand new in 2006.

Many times, but not always, after I turn on my computer from a cold startup (or even from a simple restart many times. But not always), I have to go through the process of re-pairing the key at startup.

This does not happen every time. Only sometimes. And sporadically.

For example:

Sometimes, I'll leave the computer turned off for days at a time. When it boots up, the keyboard is paired with no delay.

But sometimes, I turn the computer off then back on again (or do a functional restart), and it needs paired.

Sometimes it works fine.

And many times, there will be long periods of time that it will need to be Paired at EVERY startup.

Then long periods, where it will pair perfectly.

Sometimes weeks or months.

Sometimes days.

Is there a fix to this?

Thanks