Hi Koi, for filleting on one side the problem is a skinny little face fragment:







On the other side, the filllet that has already been placed there now makes a tighter bend for a new fillet to try to navigate through. This will limit the new fillet to need to be smaller than the previous one. If you want to have a larger fillet in that area you will probably need to fillet it at the same time as you to the other long edges instead of in a separate pass.

- Michael