Have any major glitches been discovered?

Major, no. Glitches, no. Sequence breaks, yes. Useful, varying yes and no.

The sequence breaks that are useful to speedrunning are usually on a per Rainbow Drop basis, either doing things out of order or with/without an clearly un/intended skill. Sequence breaks that skip skills take a lot of time and usually slow things down since the rooms with skills usually offer quick Drops themselves that have to be replaced. No known way how to skip chapters, since the Heart of Influence door doesn't spawn until you have enough Drops, and likely would require a glitch being found.