Tested in Essentials v18.1, if the player has a Pokemon with Truant on the field, the opposing Pokemon stops attacking after roughly three activations of Truant (so about six turns in).
It looks like Bulbasaur only knows Synthesis, which only has 5 PP. I'd guess that this bug has nothing to do with Truant, and is in fact about Bulbasaur not using Struggle when it should.