This indicates a preloader mismatch. Force stop the tool, remove the battery, reinstall drivers, and flash only the preloader.bin from a correct stock ROM first.
A red progress bar (Download Agent loading), followed by a purple bar (RAM test), and then a yellow bar (writing flash) indicates success. A green circle means "Download OK." mtk flash tool v51420 top
One of the "Top" features is its robust handling of custom Download Agents. Unlike older versions that struggled with authentication, v5.1420 allows easy selection of different DA files, helping bypass authentication on newer MediaTek devices. This indicates a preloader mismatch