Well Algaefix and/or excel,, are reported to have negative effect on a few species of plant's.And although you performed largish water changes since,,,the water changes Would in my view,, only remove what was left in the water/tank,, not that which leaves of plant's may have absorbed.
Just my two cent's.
Before I even got to the end of this thread I was thinking, that's exactly what Excel does to my crypts. That's it without a doubt in my mind. Algae fix doesn't do that to Crypts.
I could see that since crypts are slow grower. I will monitor the crypts on the new growth to see if the new leaves will be back to normal.