During my totemic druid solo run I've encountered this small bug.
After Staff of Arundel is equipped the character is given bonus spells at the 5th and the 6th levels. Meanwhile, if after resting and thus making these spells available to use, the character decides to attack with this stuff (without any switching to another weapon), he loses the bonus spells. So that to use them again the character must again choose the appropriate spells and rest.
It's not an intended behaviour. I attach the save.