Water temps here have recently dropped quite a bit to more favorable spawning temps. I wouldn't be surprised if this is what is triggering your RES to resume spawning or spawn for the first time. Surface temps were in the upper 80s a few weeks ago, yesterday my pond was 72 degrees in the morning, then 76 degrees at dusk. Water temps have dropped that much.
With the drop in water temps I have started looking for newly hatched GSH fry to show up, so far I haven't seen anything yet.
