Cannot slot Elemental Weakness

On entering abyssal depths, I removed my Elemental Weakness skill gem because of the bug described here.

I cannot slot it back, even though the equipping restriction is disabled in the options. Note that the skill UI prevents me to do so whether or not I'm shapeshifted.

Edit: the problem is unrelated to the abyssal depths; it is caused by the Dialla's Desire support gem. To slot back Elemental Weakness, I need to first remove Dialla's Desire and put it back last.