Instead, "the instruction queue is becoming overloaded and impacting performance", which seems to suggest the game's trying to process too much at once. That was apparently "a distinct discrepancy between what we observed in the pre-launch versus post-launch environment".
One thing the post is adamant about is that the huge crowds aren't to blame:
Though crowd size was something we looked at extensively pre-launch, it is something we continue to keep a close eye on. We have just finished a new round of tests on crowd size but have found it is not linked to this problem and does not improve frame rate, so we will be leaving crowds as they are.
The changes in the next patch will instead focus on parkour edge detection and making the code better at working through its to-do list. These are the revisions that should "improve framerate stability for all players":
Streamlining some technical aspects of navigation: We've fixed a number of edge cases with our detection system to smooth certain behaviours during parkour. We've fixed a few objects which were improperly tagged to smooth navigation.
Improving task scheduling: We've tuned the way the computing tasks are prioritised and parallelised by the processor cores to improve framerate in certain edge cases.
Tweaking performance for Reach High Points: We've optimised the reach high points, during the camera swooping sequence to improve framerate a little bit.