Umlaut key combo of Windows Custom Keyboard Layout stops working until reboot

I have a Custom Keyboard Layout installed that I created myself using MKLC and have used without issue for many years. Two weeks or so ago, the Umlaut A key combo I defined (AltGr + A; affects both uppercase and lowercase) stopped working on my managed corporate computer until I reboot, and from then on would only work for a relatively short time (probably around an hour) after each reboot. This almost always affects my Umlaut A key combo, but has once affected another Umlaut key combo instead of Umlaut A.