Some keys don't register when I use model 100 on MacOS High Sierra

I received my Model 100 a couple of days ago, and I flashed it with the Kaleidoscope firmware using the Arduino IDE.

I have been using it mostly on Windows 10, and have no issues with the keyboard at all, everything works fine.

I’ve also used it with a newer Mac running MacOS Monterey with no issues.

Today I plugged the Model 100 into my older 2012 Macbook I use regularly which runs MacOS High Sierra 10.13.6 (highest OS version that I can run on it) and a lot of the keys don’t register the keypresses…

For example, the F1-F12 keys won’t register, nor the arrow keys or spacebar. The letters all work, but ,./ doesn’t.

I’ve not had this issue with any other keyboard I have used with my old laptop, but this is the first one that uses Kaleidoscope.

Any ideas what might be the cause of this?