Brad Saucier

Unfortunately the only solution to the issue in that video is replacement of the main board. 
 
Fortunately non piano sounds are usually unaffected, continuing to perform as they should. 
 
Most fortunately, the piano will still function perfectly as a USB MIDI controller.  This means virtual instrument software like Pianoteq can be used as the sound source for piano, which many people prefer over the internal piano sound.  

Ideally, the device controlling port C should be sending patch select data and storing any patch setups itself.  If your device is not capable of doing that, a workaround may be possible using the MIDI recorder on the PX-560 to record mixer settings.  The MIDI recorder is the only tool on the PX-560 capable of recording port C mixer settings.   
 
I would look at Arturia documentation, look for a way to send patch select messages and save them as a preset.  The PX-560 has tone charts in the appendix which lists all of the bank select and program change data needed to select tones.  

"My Setup" stores speaker status and can also store which bank of registrations you want to use with that setup.  

On the PX-S6000, select the function button set (F Button Set) "01 Standard".  You should see Metronome as F2.  Press F2 and scroll down to "while recording" and turn that ON.  Hope that helps.  

Turn down your modulation wheel.  It's not in the off position.  All the way down is off.  
 
If that doesn't fix it, can you post a sample of the sound?  The modulation wheel may need repair.  

Yes indeed, high humidity can cause key sensor issues.  The rubber sensor membrane can stick in the closed position, causing a key trigger maximum volume.  I think as long as you bring it home and dry it out between gigs, you'll be mostly okay.  It may be reaching the age where humidity will affect it more than it used to, from more dust and dirt accumulated under the keys and such  

All is quiet.  I'm hoping they're finally working on a PX-5S replacement.  

Admin Note:  This post is marked as solution since this is the very first thing anyone should try.  If this fails, the rest of this topic may help. 
 
  Did you try blowing air in the gap around the key first?  It might have saved you a lot of work.  We've seen a number of these key malfunctions and the first thing I always suggest is air. Believe it or not, that works most of the time.  No disassembly required.

Welcome to the forums!  Congratulations on your new Casio! 
 
I listened to the samples.  Your Casio is performing as designed.  I hear nothing unusual.  The default tuning temperament is "equal".  You can select from other preset temperaments based on classical tunings.  Equal tuning is most common in music today.  You may want to research equal temperament tuning discussions on the internet, and how it's "perfectly imperfect".  It's very interesting stuff.   

Return the keyboard to the seller, or have it repaired under warranty, if it is still within warranty coverage.

Unfortunately PX-S3100 does not have user rhythm expansion memory.    

I have not seen that brand before.  It seems to have good reviews.  Have you double checked that your MIDI IN and OUT is connected to the proper ports?  With MIDI, IN connects to OUT, and OUT connects to IN.  

It doesn't have to be aimed with any precision other than between the problem keys, somewhere in the middle.  Canned air is sometimes not even needed.  I've done it by blowing between the keys myself. 

As long effects settings and mixer settings are the same, stage settings can switch seamlessly.  If you want to switch effects and mixer levels, it's best to cross between two zones rather than stage settings.

As we see in the chart, "Strum 1" is listed under Preset Tone #169 Versatile Nylon Guitar.  The chart shows Strum 1 is assigned to note C7 and will sound when played within the velocity range of 1-127 (the full range).  
 
To play this sound, press the tone button, select tone# 169 Versatile Nylon Guitar.  Octave shift the keyboard as needed to reach the C7 note and press that key.  You will hear a muted strum noise. 
 
Now to be clear, "strum" does not mean a chord will be played on a guitar, or a rhythm will be played. The "strum" sample is simply an effect sound.  It's the sound of muted guitar strings played with a single strum motion.  These samples are in the keyboard mainly for use by programmers creating preset rhythms. 

Those are not host devices.  The CT-X5000 requires a host.  You'll need a standalone host box specifically designed to connect USB MIDI keyboards to other keyboards.  This is because USB is not specifically a musical instrument port, like 5 pin MIDI is.   

MIDI CC11 "Expression" is the function an expression pedal will control, literally as the jack label suggests.  It is not "assignable" to other functions on the CT-X series.  Note, Yamaha pedals have been found to be incompatible with Casio keyboards.  

Turn off your modulation wheel.  Down is the off position. 

Is there a reason you are using the internal recorder as an intermediate step rather than directly record to logic?  
 
Once a song is recorded to the MIDI recorder on the 1000V, you can export the song to a USB flash drive as a standard MIDI file, then import that to logic. 
 
Note: Due to the MIDI file format, MIDI recorder songs will convert to SMF in two ways.  Excerpt from user manual below explains....
 
"When saving Multi-track Recording data as a standard MIDI file (SMF), only the system track data is saved if the system track contains data. If the system track does not contain any data, only the solo track data is saved."

The manual says hold the up and down tempo buttons. 
 
Which tone is it stuck on?  What does the display show as your upper 1 tone? 
 
Are you sure the modulation wheel is in the off position?  It should be all the way down, not centered like the pitch bend wheel.  

Press edit>stage setting>common edit>pedal edit>.... you'll find the settings there.  

After a factory reset, it should not be out of tune.  How have you determined that it is out of tune?

Line out does not mute the speakers.  Only the headphone output does that.  Are you sure line outputs muted the speakers?  Note, volume level of the speakers and line out is controlled by the main volume knob simultaneously.  

Chorus is a system effect, not a DSP effect, so yes, chorus and Active DSP can be used at the same time on a tone.  
 
Active DSP is a combination of preset DSP effects called "modules".   The ability to combine effects lies solely in selecting a preset Active DSP which contains the effects you want.  If an Active DSP contains an effect module you would prefer not to use, the ability to turn off individual modules is provided.  

Those are not headphones jacks.  Those are line output jacks and not suitable for headphones.  The headphone jacks are in front, near the pitch bend wheel.  You will need a mini plug adapter.