I'm not seeing a correlation but here are the following ways trees (may) not be cut in one swipe because of:

• How the player is looking at the block being mined?

• Which block is checked after the block is broken?

What I do know is:

• Once it does cut all adjacent logs, it breaks all connected logs. It even breaks diagonal logs which aren't connected by any sides to the logs that are meant to be broken.

Again, I haven't reached into the code to decipher the problem myself but here are the points for the Tree Feller for issue documenting anyways.

Further look into it, I again see no correlation in the swings I took with the item...

Also:

• Durability only takes into account of the log you broke, not calculating the connected logs broken.

No idea, didn't code it.

Hmm, once I get the dev env going I'll recode tool mechanism.