Low tech plant wall of text incoming.
One of my favorite neutral-soft water lower canopy/divider plants; Windelov (lace) Java Fern is a self cloning (apomixis) rhizome plant. The babies that grow on the leaves originate as small nodes. The things I have observed impacting the health of windelov are: low or high water flow, low CO2 concentrations, low mineral balance, and low nitrogen levels.
The CO2 levels (dropping) in a low tech tank can be affected by significant change in stocking, other plants added to the system up stream, or changing spray bars/filters/air stones. The flow to the plant from airated water can be interrupted by other decor as well.
Total Nitrogen can be over reduced by cutting stockings and not reducing your water change/cleaning/husbandry habits. Also by changing fertilizer brands/types if that's your thing.
Mineral balances can change drastically for those of us on well water seasonally, also can be caused by city/municipalities starting up new water treatment systems, or adjusting seasonally to account for different conditions in the pipes.
As a lower canopy plant, windelov doesn't require a ton of light, but if you were to cut it down in the hours per day cycle you could see some dormancy for a "season".
There are 2 things that tend to force java Fern into producing nodes, one is high quality (in it's opinion) conditions, the other is starvation or sudden but permanent change in parameters. When changing parameters a self cloning plant will often send out as many nodes as it thinks it can feed using itself as food. This survival method allows a plant to produce babies and send them down stream for a better chance of species survival. Even if the mother plant does adjust and end up surviving the nodes have been triggered and will grow to maturity. If you take those mature nodes and replant them in similair water/flow/lighting they will likely just grow normally, if any of the parameters are significant they will repeat the self preservation cycle.
It's possible that after a few generations in your tanks you have moderate/good conditions and they are not self preserving as they have acclimated, but that also they are short abundant CO2 (on a low tech standard) or total nitrogen so they are now growing more slowly/steadily.
Good news is that you can still propagate by cutting the rhizome, and much like Anubias you can predict the direction of growth to continue to run the original direction on both the cutting and the original. That can help in strategically making walls if your substrate is appropriate for the roots to take naturally, the plant has a real knack for keeping it's rhizome just above the surface preventing rot while still rooting nice and deep into the soil.
Visual aids (maybe some reading this haven't discovered the joy of lace Java Fern)
Windelov
Rhyzomes that had previously been cut continuing to grow from right to left, keeping the rhizome at a healthy height, while still sending nice roots down.
