Lightroom Classic slow to start / window redraws slowly – cause: Avast "Do Not Disturb Mode"

Lightroom Classic 15.6 on Windows 11 (26H2) took 30–56 seconds to start, showed "Not responding" in the title bar during startup, and you could watch the window being rebuilt after minimizing and restoring it. Strangely, if I started Lightroom immediately after Windows booted, it was fast and stayed fast for the whole session.

Cause: Avast's "Do Not Disturb Mode". It appears to monitor every program started after Avast's user interface has loaded, including every window Lightroom creates. A Lightroom started before Avast's interface loads is not affected, which explains the "fast right after boot" pattern.

Fix: Avast > Menu > Settings > Do Not Disturb Mode > switch it off. Result: catalog open in 12–14 seconds instead of 30–56, also when started late, and no more slow redraws. I confirmed it by switching the mode back on (slow again: 56 s) and off (fast again).

Things that did NOT help, in case you're trying them: - Pausing Avast shields or adding Lightroom exclusions (the Do Not Disturb Mode keeps running) - New catalog, reset preferences, GPU driver update, display scaling - Clean boot, new Windows user account - Separate SSDs for catalog and photos, sfc /scannow and DISM.