Seems like Blizz might have offset bank bag numbers by 1, Player Bank Bag 7 no longer being found by Bagnon.
Had to use workaround for GetBankBagSlotFlag as per AtreyuGreen's comment in #1461

Only one issue still remaining is that the remote version of the bank where you can see your bank wherever you are, but obv not interact with it, still has the last bag missing (shown empty on the bank bag bar) and the bag slots themselves also not shown inside the frame. So that number fix for the for loop with the (+1) seems to be affecting the regular bank interactivity with Bagnon, but not the remote "copy" that you can see even if you are not next to a banker.

I tried to fix it, but I am not that good with lua. :) Appreciate the progress so far and I can actually live without the "remote preview" of the bank, but since you guys are good at finding fixed I figured I'd mention it, in case someone can find how to resolve that as well. :)

Thank You!

Yes it does seem to be an issue with the numbering being slightly different.
Interface\AddOns\Bagnon\common\Wildpants\classes\bank.lua:12
for slot = 1, NUM_BANKBAGSLOTS do tinsert(Bank.Bags, slot + NUM_BAG_SLOTS+1) end

This (mostly) fixes the bank and shows all bags.

Yes it does seem to be an issue with the numbering being slightly different. Interface\AddOns\Bagnon\common\Wildpants\classes\bank.lua:12 for slot = 1, NUM_BANKBAGSLOTS do tinsert(Bank.Bags, slot + NUM_BAG_SLOTS+1) end

This (mostly) fixes the bank and shows all bags.

Brilliant! Can confirm this fixes the bank bag 7 issue

After a bit more messing, I think I have a solid fix. I pull requested this to the authors but until they accept or implement it themselves another way, you can see the changes necessary here:
Jaliborc/Wildpants#85

@Hinos you need to make a similar change in BagBrother too

Change these two lines at the top of BagBrother/Code/Events.lua

local FIRST_BANK_SLOT = 1 + NUM_BAG_SLOTS
local LAST_BANK_SLOT = NUM_BANKBAGSLOTS + NUM_BAG_SLOTS 

to

local FIRST_BANK_SLOT = 1 + NUM_BAG_SLOTS + 1
local LAST_BANK_SLOT = NUM_BANKBAGSLOTS + NUM_BAG_SLOTS + 1

tl;dr: blizz added another bag slot but never incremented NUM_BAG_SLOTS so it needs a slight adjustment.