Its strange because something similar (but to a lesser extend) is happening so several species of mine right now, leaving me clueless.
Root issues would originate from over watering and I suspect it is rather unlikely that you overwatered all your sallies at once. The same issue showing up on all plants more or less simultaneously makes me suspect fungus gnats.
But maybe the leaves were first burned by some factor (dry air, heat, light, spray) and little later the dead material can be expected to look like yours, creating the impression things that simply were attracted by already weak / dead material were the cause of the damage. So fungus could have come later if there is any.
As damaged as the leaves are I would remove them if the plant is healthy besides the leaves. They are of little use but potencially dangerous. Also if they drop into the pot. The plant, if healthy, should easily produce new leaves.