Hornwort Troubles

[Haiven]

What do you guys know about hornwort? It has been growing happily in 8 of my tanks for several months, and all of a sudden, simultaneously in all my tanks, has started to turn brownish green and shed leaves. The tank temp, lighting and ferts haven't changed.

Is this normal, seasonal, and something I should ride out, or is it dying and should I ditch it all?