Garageband recording latency

Recently I've started getting serious latency on Garageband where there's never been a hint of an issue before.

I've got, for instance, a project with four unmuted tracks (six muted). All plugins are turned off on each track and the master. Still I have a crazy amount of latency on the front end.

The interface is a Focusrite Clarett 4pre which is clearly receiving the signal as quickly as it should. The computer is a mid-2011 Mac mini running High Sierra and Garageband 10.3.5. No other operation of the computer has any noticeable issues. The activity monitor registers around only 15% of the CPU being used.

I've tried quitting all other programs, restarting Garageband, restarting the computer, unplugging all of the inputs, changing the input/output in Garageband, all multiple times, but no luck. Only some of my Garageband projects have developed this problem, but once they do it looks like it's irreversible.

PLEASE HELP!