It seems like connectors can have over 1000 items and not back up. I am not sure but I think the way your connectors work are they have a single inventory slot (or possibly more) and it stores items coming in and outputs items every second or something. But atm we have a mod I guess that changes stack sizes to the thousands. So it will take a while to see if it can back up or if it just holds a stack of items.
It seems to have backed up. The amount of iron plates in it was 8006. So it can hold 4 stacks of items. I suppose this is less of a bug and more of a mechanic
There are 2 hidden chests per connector, one above ground and one below ground. By default they each hold 2 stacks, but you can change this in the mod options.
