I'm still trying to figure out what OP has been up to,...

I'm still trying to figure out what OP has been up to, especially given they are long MLX via swaps as well. My guess is the following: MLX must be a sizable position in OP's portfolio. For some reason they need to raise cash. OP decides to sell MLX stock to raise cash but wants to retain MLX long exposure (at least initially) buy being long MLX via equity swap. Enter a friendly investment bank, BAML. They buy the shares from OP and take the short side of the swap. That's how BAML ends up being a substantial holder via its newly acquired inventory of MLX shares. Why does BAML do this? They can earn fees & interest in 2 ways: 1) financing terms of the swap and 2) lending MLX shares to short sellers.

However, at some point OP clearly decided to reduce its MLX equity swap exposure. On this bit I'm a bit hazy, but I think selling down the swap position does not trigger reporting requirements. Previously OP disclosed their swap position on a voluntary basis because it was so big that they were in a regulatory grey area. Now what does OP selling MLX swap do? Typically you unwind the swap with the same counterparty you started with, namely BAML. BAML would need to sell MLX shares from their inventory and unwind (i.e. buy back) a portion of the swap that OP is unwinding (i.e. selling).

In the above scenario all the mandatory reporting needs to be done by BAML and (I think) none by OP. OP only needs to report if they still have cash equity to sell - which may also be the case.