Following numerous reports of MacBook Pro laptops aggressively throttling the CPU to keep temps in check, Apple has come out and acknowledged the issue, blaming it on a bug in the firmware, and issued a fix. It also apologized to affected customers who "experienced less than optimal performance on their new systems."

The issue drew widespread attention when a YouTuber David Lee posted a video showing a premium MacBook Pro configuration with a Core i9-8950K inside. Within a few seconds of running Adobe Premiere, it would throttle to below the processor's 2.9GHz base clock.

YouTube via David Lee. Click for original. (Image credit: YouTube via David Lee)

"After a few seconds, we're starting to see some very serious throttling... This [Core] i9 in this MacBook can't even maintain the base clockspeed. Forget about turbos and all that stuff, it can't even maintain the 2.9GHz base clock, which is absurd," Lee states early in the video.

Buying a 15-inch MacBook Pro is one of the ways you can get your hands on a Core i9 chip. It's offered as an optional upgrade, which brings to the total cost to $3,099, or higher if you opt to bump up the RAM and storage as well. While expensive, you end up with a powerful laptop sporting a Core i9-8950HK processor inside.

So why is it so quick to throttle, which in turn negates that pricey performance upgrade? Lee blames it on the chassis and its inability to properly cool the chip. According to Apple, it's a firmware bug.

"Following extensive performance testing under numerous workloads, we’ve identified that there is a missing digital key in the firmware that impacts the thermal management system and could drive clock speeds down under heavy thermal loads on the new MacBook Pro. A bug fix is included in today’s macOS High Sierra 10.13.6 Supplemental Update and is recommended," Apple said in a statement.

"We apologize to any customer who has experienced less than optimal performance on their new systems. Customers can expect the new 15-inch MacBook Pro to be up to 70 percent faster, and the 13-inch MacBook Pro with Touch Bar to be up to 2X faster, as shown in the performance results on our website," Apple added.

Apple isn't sharing what exactly the "missing digital key" is or what the update specifically did to fix the problem. It sounds like bad firmware, and how it slipped past QA is one of the major questions. One thing to note is that the issue affects all MacBook Pro with Touch Bar models, and not just the ones with a Core i9 CPU inside.