A three month rest seems to be enough for Olea europaea "little Ollie"
(Montra). Olives need _lots_ of light. Here approx.: May-Nov. outside,
Dec.-April inside under lights. If you can provide cooler night temps.
inside so much the better. Well drained soil.
Asuming nothing else is going on...loss of leaves(that shoudn't drop) is
just a result of low light levels. While evergreen, leaves don't last
forever.;-).

Alan

Blue Mountain Bonsai
Ontario, Canada
Zone 6