I noticed a bug with Shillelaugh today when casting it on my 2(1d6) wooden quarterstaff.
There was no damage increase at all.
The Shillelaugh buff icon apeared in the upper corner but the buff description on the icon did not apear and testing the damage on some enemys confirmed that.
Then i tested it on a normal 1d6 wooden quarterstaff and the spell worked fine.
Tested it also on some other wooden weapons like scepter and greatclub.Did not work on them when the damage profile was better then normal.
It seems whenever the weapon has an enhanced damage profile like all the level 20+ loot gen weapons, it is not working.