Audition's interface "frame rate" drops during playback

Can't seem to find anybody else with this problem, hopefully someone here can help.

When playing back a track in Audition, the frame rate of the video (as in, the actual visual feedback you get as the playhead or track scrolls) gets progressively worse. Audio plays back normally--no jittering, stuttering, nothing like that. But the playback head and the level meters start to drop frames.

When I first open the program, the problem is either not present or (more likely) not noticeable. But it returns within a matter of minutes and gets progressively worse. Within about 10-30 minutes, it gets so bad I can't pick edit points or monitor the levels visually and have to relaunch the program.

I'm using Audition 11.1.0.184 (currently up to date) on a MacBook Pro:

High Sierra (10.13.4, also currently up to date)

2.9 GHz Intel Core i7

16 GB 2133 MHz LPDDR3

Intel HD Graphics 630 1536 MB

This doesn't happen with any other application, so I assume it's not my graphics card or anything like that. I have deleted and reinstalled Audition CC already; the problem recurs along the same timeline (10-30 minutes of playback).

It happens on single-track mono sessions with no other programs running, so I know it's not a memory or processor problem.

Anybody know what this is? Anybody ever even heard of this problem? Any help you can give is much appreciated. Thanks.