Bluetooth Keyboard Latency

Has anybody encountered an issue regarding Bluetooth Keyboard Latency?

One of our clients just had their iMac's Fusion SSD replaced, and since they got it back, the bluetooth keyboard will intermittently lag. What I mean is that sometimes, typing brings characters up on screen in real-time. But sometimes, typing a whole sentence will yield no characters until a few seconds after typing stops, then the whole string loads up at once. Or, sometimes a character will repeat on screen several times despite only 1 press on the keyboard.

This did not occur prior to the Fusion SSD replacement.

On a very related note, my person Mac Mini's (a 2014 & a 2019) both exhibit the very same behaviour, and have since they were both new. I have 2 different Apple BT keyboards and a Dell WK717 BT keyboard, and all 3 behave the same way on both Mac Mini's intermittently.

It's very baffling. I've always dealt with it, but I can't just tell a client "to deal with it" unfortunately...

Help?