Korg x50 after hitting some notes, regardless of patch, the sound output triggers a fluctuation of the note, as though the keyboard is possessed. This recently happened November 2017.

SOURCE: psr e303 yamaha double sounds

Do you cover the keyboard when not in use as small particles of dust can make their way in between the keys?

You can try blowing any obstruction out with a can of compressed air, may solve your problem.

As I'm not familiar with this Model, does the keyboard have 'touch response' on board? If so there will probably be a 'Contact' strip made out of tubular rubber under the keys and this can sometimes 'burst' especially on a certain key that is played most of the time. For example if you play mostly in the key of 'G' or keys that use that note....

Hope you find this helpful......

SOURCE: MIDI Keyboard note delay problem, not latency problem PLEASE HELP

You are suffering from midi latency. There is a good article about this at www.thewhippinpost.co.uk/latency.htm There is also some good advice there.

SOURCE: I connected my Casio CTK

Oh, oh... that is often called the "Dreaded MIDI Drone".

There ccan be more than one causes, however two of those are this:

1. The receiving device either does or does not respond to the note off command or only responds to the note on command with zero velocity, which is also now interpreted as note off. Check the MIDI implementation chart to determine this.

2. Two MIDI commands have merged without using a MIDI merger which makes sure ONLY complete MIDI commands are sent. If the commands are mixed, dreaded MIDI drone is assured.

SOURCE: KORG SP-250. Keyboard powers

There is probably a cable loose that connects the keyboard itself to the processor... OR the key contacts have been contaminated by spilled liquid. The keys are scanned as a matrix. The contacts will be a conductive rubber pressed against circuit board traces. Clean contact "pills" and the circuit traces with ONLY 99% isoprophyl alcohol.
This is NOT for the unskilled to attempt a DIY other than carefully opening and looking for a cable that has come loose.

SOURCE: My Casio Px 330 keyboard

This is a problem with one of the two contacts for that key. The contacts close at different times as the key is depressed and the time it takes between is measured as velocity which is used to control the loudness as in a regular piano. The contacts are conductive rubber pills. After a lot of dis-assembly you can clean them with 99% isoprphyl alcohol and Q Tips. Clean both the pills and the circuit traces on the board they are pressed against. Be very careful of the ribbon cables between the halves of the case.