If the camera exposure settings were truly manual, the most likely sources of variation were not shutter/aperture/ISO, but flash output, autofocus behavior, and auto white balance.

For best consistency in a sequence:

• use manual white balance instead of auto WB, so color doesn’t shift between frames
• switch focus to manual after focusing, so the camera doesn’t refocus shot to shot
• set the flash to manual power instead of an automatic flash mode, which can vary output between frames

Also, AE lock isn’t needed when you’re already in manual exposure mode, and AF lock isn’t needed if you use manual focus.

Evaluative metering won’t affect exposure once the camera is in manual mode, but it can matter if any automatic flash metering is involved. If depth of field is tight at f/4, consider a smaller aperture if your lighting allows it, so small subject movements don’t change apparent sharpness.

In short: lock white balance, focus, and flash power manually for the most repeatable results.