Windows Update Service stalls with 0x8007045E during concurrent installation requests

Observed failure

When multiple Windows Update installations are queued simultaneously on Windows 11, the Windows Update Service can stall and return error 0x8007045E. Event logs show a ConcurrentInstall warning and the UpdateEngine process may enter a deadlock state.

Constraints and uncertainty

This behavior has been reproduced on builds 22H2 and 23H2 by launching two Start-WUInstall commands in parallel, but the error code is not officially documented as concurrency‑specific. Hardware, driver stack, and third‑party services can influence whether the stall occurs.

Open questions

1. Is the 0x8007045E error a deliberate serialization mechanism or an unintended deadlock in the UpdateEngine?
2. Which internal lock or resource (database, download cache, background task scheduler) is the contention point?
3. Does the ConcurrentInstall warning precede the error in every case, or can the stall happen without a logged warning?