Faulty Kenko 2x Teleconverter

Ok, so with all the new information here are some new sample photos.

But firstly, I noticed that the eyepiece exposure level and the live exposure level measured the light completely different even when i had the exact same settings (including MF, checked via live view 5x, spot metering on blue bottle) for everything else!

No TC, EXIF f5.6 exposed via eyepiece level (cropped) - maybe tiny bit bright for it being eyepiece level and no tc (?), but sharp (if i slightly adjust exposure in lightroom, looks fine)

No TC, EXIF f5.6 exposed via live view level (cropped) - too dark, but sharp (if i adjust exposure in lightroom, looks fine)

TC, EXIF f11 (f5.6 aperture) exposed via eyepiece level - looks unsharp and too bright but if i adjust exposure in lightroom (and for some reason wb as that changed 2 seconds later!?) it is acceptable (see image right under this one as edited version)

TC, EXIF f11 (f5.6 aperture) exposed via live view level - sharp and good exposure. Looks like live view exposure is the best to use when using the TC; as an unedited image is the best out of the 3 even without the TC.