As one more voice in the wilderness...

Good video. I think you're messing with the coffee too much - resulting in an inconsistent puck density - which you see mostly as edge channeling and an under-extracted center.

Try this. Put the basket in the PF. Weigh the beans prior to grind. Grind your weighed dose. Dose/thwack vigorously directly into the PF/basket. Now do as little as possible w/the coffee prior to the tamp. Lightly - no tapping, shaking, stirring etc. - move the coffee so as to make sure you have at least as much pre-tamp depth around the edges as the center. Now tamp - more or less as firmly as you already are. That's it. See if the center gets extracted now.

And if that seems to help. it looks like you may need to updose another gram-ish - and maybe open the mazzer a scootch to offset that...