Hello Wade - reverb and release are so similar I often confuse the two?

Thanks for the response.
Reverb. Even with the reverb turned off, if I strike a chord and quickly release the keys, then depress the sustain pedal, the residual reverb still kicks in. It would seem the sustain pedal is activating the reverb separately. And I can't figure out how to turn that off.

The only sustain strangeness I've noticed thus far was related to holding sustain on a struck note, then restriking (and holding) the same note (or notes) softly while sustain was still held - then letting go of sustain. With previous firmware, this would suddenly make the restruck notes softer. I saw a firmware update release note which mentioned something about making the piano respond more realistically to the sustain pedal which I assumed was related to fixing this issue. Although perhaps something else was broken in the process. I have not tested any more recent firmware.

https://yamahasynth.com/forum/montage-sustain-response-pianos

It would be strange to activate reverb. On a real piano, pressing the sustain pedal might make all the strings ring with some soft harmonics as the dampening felt lifts off the strings. Not sure if there is any attempt to make this a "feature". Seems they (Yamaha) wouldn't recreate this just like there's no thud of the pedal being pressed (items in the extraneous noise category).

Not being able to test this right now - the keyboard is packed for a performance - I am wondering if the half dampening is turned on for "CFX Concert" and if pressing the sustain while in the release portion of the envelope may cause an issue. If the half dampening feature is turned on - try switching that off and see what happens. Right now that's just a theory of a possible corner case of pressing the sustain pedal while the EG is already in the release portion of the envelope.

Might be the Damper Resonance designed to reproduce the acoustic piano's own reverberation chamber in the harp... it is linked to the Sustain pedal.

Damper Resonance - Insertion Effect
This is an Insertion Effect algorithm that reproduces the rich harmonics and unique sound characteristics of an actual grand piano when using the damper pedal.
This effect algorithm intended for use with acoustic piano samples, can be applied to any sound (with varying results). However, when used on the acoustic piano Voices you can add a very realistic sound-board simulation effect which is related to your use of the sustain pedal.

Experiment: You can isolate the soundboard effect by making the DRY/WET value "D/W63", completely wet, then step on the sustain pedal while playing to bring in the soundboard.

DamperResonance
By setting "D/W63" - This is like hearing just the soundboard resonance. You can hear how it is "biased" to the sustain pedal (Damper Control) - in other words, there will be no sound at all until the pedal is activated. Setting "Damper Control" to anything more than 0 makes the soundboard resonance less biased to the pedal's position. Using the FC3 to control this Damper Resonance you can control the amount continuously. The "Pedal Response" (PedalRsp) is the time it takes the soundboard's 'aura' to rise to full volume in response to the pedal going down.

Once again subtlety is important for realism. Soundboard resonance is best felt rather than heard. And while it is a kind of reverberation that takes place inside the piano verses the kind that happens outside in the room environment.