Very High CPU Utilization When Using Masks/Brushes on iMac

Lightroom Classic: 12.1

MacOS: Monterey 12.6.2

iMac: Late 2015 with Retina 5k 27" 

Processor: 3.3GHz Quad-Core Intel Core i5

Memory 32GB 1867 MHz DDR3

Disk: SSD

Graphics: AMD Radeon R9 M395 2GB

Step 1: In "Develop" mode, after performing some crops, I will add a "Mask" (usually in either "Subject" mode or "Objects" mode, but I have tried traditional "Brush" mode as well, and it exhbits the same behavior).

Step2: After adding mask, I'll change the exposure, contrast, etc of the mask(s)

Step3: Get out of Mask mode, and start performing additional edits (changing temperature, vibrance, whatever... doesn't really matter)

Expected: All should continue working with no lag/slow-down.

Actual: Lightroom Classic starts slowing down, and exhibiting the "spinning" progress indicator (on almost every movement of the mouse). If I try to change settings, for instance, it takes tens of seconds sometimes to show the "impact" of the changed setting (and the spinning wheel keeps spinning).

Troubleshoot: I pull up the Activity Monitor, and Lighroom Classic is up over 200%, sometimes over 300% and it does not go back down.

Troubleshoot2: If I select (in the Development History panel) the step prior to adding the Mask, and wait for about a minute, the CPU goes back down. If I then select any "Mask" step (or beyond) in the History panel, then the CPU jumps back up to ~200-300% usage.

Troubleshoot3: I've noticed that I cannot always get this to happen, but it happens on at approximately 7 out of 10 images that I apply masks. Also note that once it happens to a given image, I cannot do anything to that image to alleviate the issue (I've even tried to delete all of the masks, but then the minute I add a new mask again, the CPU ramps back up).

I have tried various performance enhancement techniques (as specified on the Adobe site), and nothing has seemed to work.

Note: I do not recall having this issue on previous version of Lightroom Classic.