AfterFX.exe terminates while idle in the background with a project open

Issue
After Effects 26.3.0.87 hard-quits while idle in the background (no render, no preview, no user interaction; focus in another application). Exception 0xc0000409 FAST_FAIL_STACK_COOKIE_CHECK_FAILURE (stack buffer overrun detected, fail-fast via int 29h) in dvacore.dll. Captured twice via WER LocalDumps in different projects: both minidumps show the IDENTICAL WinDbg failure hash {b7cd505e-b164-73b2-29c1-7bd10998cdc0} and identical faulting address dvacore+0x340e1d, so this is one deterministic defect, independent of project content.

Faulting thread (both dumps identical, export symbols only):
  dvacore (fail-fast at dvacore+0x340e1d)
  dvacore!dvacore::threads::MultiTenantRecursiveMutex::UnlockFromReading
  dvacore!...::ScopedReadLockWrapper::~ScopedReadLockWrapper
  MC!MC_Stuff::IsInMemory
  MC!MC_Stuff::~MC_Stuff
  MC!MC_Stuff::`vbase destructor'
  BEE!BEE_WorkQueue_RegisterListener (+0x4eab)
  BEE!BEE_ItemFinder::GetItem (+0x13940)
  BEE!BEE_RenderState::WorkQueue_SetItemCurrent (+0xe46b)
  BEE!BEEp_WorkQueue_GetRenderGuidWithRO (+0x1982)
  (background work-queue thread created via dvacore::threads / MEE)

The crash occurs while destroying an MC (media cache) object from a BEE work-queue item, during release of a read lock. Stack analysis across both dumps: identical code path byte-for-byte; the only varying values are heap addresses and two per-session counts (~57k-70k and ~7k-13k) in the faulting
lock-release call. Process uptime was 505 s in one crash and 5,178 s in the other, so not time-accumulated. Both crashes were preceded by roughly a minute of system-wide input lag, suggesting heavy AE background activity immediately beforehand.

Steps to reproduce
1. Open a project.
2. Leave After Effects idle in the background while working in another
   application.
3. Wait (minutes to hours). Occurred twice in one working day, in two
   different projects.

Expected result
After Effects remains stable while idle in the background.

Actual result
AfterFX.exe terminates with exception 0xc0000409 (fail-fast) in
dvacore.dll. No crash-recovery dialog; the process hard-quits.

Screen recording
Not applicable (background crash with no UI interaction). Two WER minidumps
plus full WinDbg !analyze -v output are available; attachment exceeds forum
limits, share link available on request.

Adobe After Effects version
26.3.0.87 (June 2026 release)

Operating system
Windows 11 24H2 (build 26100)

GPU driver version
NVIDIA Studio Driver 595.79 (RTX 4090)

Video format
Not playback/export related. Projects contain mixed footage including
ProRes 4444 and MP4 files and EXR image sequences

Comparative information
- Affects multiple, different projects (identical crash fingerprint in
  both captured dumps).
- New/empty projects untested; crash requires extended idle time.
- Already eliminated: Compressed Frames (Lossless) disabled, Cache Frames
  When Idle disabled, media cache database fully reset, all cache locations on local NVMe with ample space, no WHEA/hardware events, RAM separately validated.