In wake of your reply on a PR I submitted on ZMK, I went on investigation.
It took me a while to understand what you were talking about (hence the confusing replies), but I think I understand your issue now, so I took the liberty of checking out your nrfmicro schematic.
I assume you were talking about D1 in the schematic of the nrfmicro.
It seems D1 uses a SOD-123 package, and according to this datasheet the 1N5819 has a forward voltage of ~0.4V at 0.6A (max LDO current, but 28 SK6812s may draw more than that), and with a typical thermal resistance of 250 degC/W, this results in a package temperature rise of 60 degC.
Thus it seems that it is indeed the cause of the heating problem you experienced.
The solution would be using a diode with a lower forward voltage and/or lower thermal resistance.