This vertical axis is auto-binned by design so that there are not too many nodes on the vertical axis. This is because having a very large number of nodes in the vertical axis hierarchy can be very expensive and can cause performance issues in large data sets.
To un-bin the column, use one of the following two options:
1. Click twice to switch from auto-binned to not-binned:
or:
2. Un-check the auto-bin box in the column selector dialog: