[KevinH]

Also, do you have any environment vars set to change the Update Page interval?

    // allow user to override the default Preview Timeout (integer in milliseconds)
    QString new_timeout = Utility::GetEnvironmentVar("SIGIL_PREVIEW_TIMEOUT");
    if (!new_timeout.isEmpty()) {
        bool okay;
        int timeout = new_timeout.toInt(&okay, 10);
        if (!okay) {
            timeout = 1000;
        } else {
            if (timeout < 1000) timeout = 1000;
            if (timeout > 10000)timeout = 1000;
        }
        settings.setUIPreviewTimeout(timeout);
    }

If not, try setting that environment var to something shorter like 500 and relaunch Sigil.

If the problem persists then the issue is not Timer related and is caused by lost or delayed change signals.