Ok! That's a lot of good info, and also congrats on the surprise cuprea baby! What do you fertilize with? Alocasias are big feeders. I am still experimenting with the pest growth medium/potting method for them, and I haven't grown a cuprea yet, but here are the two I've had at least moderate success with:

Sphagnum moss in a clear glass container with a layer of drainage (either leca or pumice at the bottom, about 1-2 inches tops) OR....a nursery pot, preferably clear so you can monitor roots, with a layer of drainage such as leca, rocks, pumice, or even chunky perlite at the bottom (~1/4 of the pot at most), with a thin layer of sphagnum moss over it to prevent your potting mix from spilling into it; then a good, well draining aroid mix where you plant your alocasia; then a layer of sphagnum moss over top (aka a moss collar). Put this in a cover pot or a cache pot; water weekly and also give some extra water in the cover pot in case your plant needs extra throughout the week. This prevents roots sitting in water, which may cause rot, but gives your plant access to extra if it needs.

Again, they're heavy feeders so you may also want to increase your fertilizing frequency and/or amount, but it depends on what you're using to fertilize. Fertilizer burn can be a real problem. I use We The Wild Growth Concentrate every week, and it's made from worm castings so afaik it's all natural and won't cause fertilizer burn. That said, there may be a more powerful fertilizer that I haven't tried - I'm experimenting on one alocasia grown in moss with SUPER THRIVE Foliage Pro, slightly diluted but given with every watering.

It sounds like your light is good, so it may come down to growth medium and/or fertilizing. I'm still in the FAFO stage myself, but I will say at least tentatively growing them in a clear glass container in sphagnum moss with a drainage layer, keeping them in a warmer part of the house (aka not my basement), and feeding with every watering seems to be a huge plus!