An update to the Three Point Arch Tool has been released, 0.1.2 (for 2.80) and 0.0.4 (for 2.7x)
The updates are on the same downloads page as usual.
This update is a bug fix to correct problems that were reported with the snapping code in 2.80, but, to play it safe, I back-ported the bug fix to the 2.79 version as well.