Lauren, reverse cycling is exactly the right name for this, and the direct answer is that it is common, it is generally a temporary adjustment rather than a problem, and an 8 month old who is feeding freely at the breast morning, evening, and overnight is usually getting what she needs across the 24 hours even when the daytime numbers look alarming. The gauges that count are the same ones as always: plenty of heavy wet nappies, her usual stools, and her weight staying on her own curve. If those hold, the clock is not the measure. If nappies drop off, or she is unusually flat or sleepy, that becomes a conversation with your health visitor or doctor rather than a forum, and I would not wait on it.
What is happening underneath: a baby who dislikes the bottle, or the setting, or simply prefers you, will often take the minimum in the day and then make up the full intake in the hours you are available, and the night becomes the main meal. Babies are very good at this. It typically settles in a few weeks as she accepts the bottle and the routine, usually 2 to 4 weeks, though some babies keep a version of it for as long as they are in childcare. Hollie's point about how the bottle is offered is where I would start: a sitting position, the bottle held horizontal so she works for the flow, pauses to let her stop and start, and offering when she is calm rather than frantic. The guide to bottle feeding a breastfed baby describes paced feeding in detail, and it is worth asking nursery to read it. At 8 months, a cup or open beaker in the day is also a perfectly good alternative to a bottle for a baby who has decided bottles are not for her.
On your pumping numbers: a fall from 150 to 100 ml a session in the first fortnight back is a very ordinary pattern and does not mean your supply is falling by a third. Pump output responds to stress, to a rushed session, to a different room, and to a baby who has moved her demand to the night, where she is taking more directly. Supply follows demand across the whole day, and she is providing plenty of demand. Keep the work sessions going at roughly the intervals she would have fed, because they protect daytime production, but judge supply by her nappies and weight and by the trend across weeks, not by one week's bottles.
Two practical points and one boundary. First, do not add more milk to the bag in response to the 40 ml; she is not taking what you send now, and a freezer full of untouched bottles is demoralising and wasteful. Second, the nights are a genuine cost to you, and feeding safely when you are this tired matters: the piece on night feeds and breastfeeding has the safe sleep section that I would ask you to read tonight rather than later. The boundary is the one I give everyone: your baby's weight and intake are for the professionals who can see her, and if anything about her worries you, a face to face check beats any reassurance here, mine included.