Sounds like poor CO2, not enough to have issues with some stronger species, but with some species, they are hurting.

If the biomass has increased say 25%, so will the CO2 demand.
This effects certain plants at different rates and to different degrees, not all plants are the same in their CO2 demand/responses.

Java fern often turns black when slightly poor CO2 is supplied with many other plant species. Small tips and melting are other signs.

Yes, you can have plant issues without quite having algae issues due to CO2.
Plants respond first, followed by algae.

If you already have algae, that's another case.
But with a decent tank to start off with, then you have some stunting, melting, blackening etc, then CO2 is fairly suspect, EI addresses the main issues for nutrients other than CO2, so that's fairly easy to rule out a limitation with many species, but low or varying CO2 is quite another matter.

Regards,
Tom Barr