There's more information available than what's obvious, but only very recently has the question been tied to something about which we have actual detail.

From what's been exposed, just today, it's apparent that there will LARGE currents flowing each time the display is updated, and even with just 1 meter of cable, that amount of current will make a lot of noise. The clock must be protected from that noise, and, of course, since, presumably, a separate supply is used to power the LED's than is used to supply the logic, while the GND is also presumably common to both, the large currents through the current-sinks will cause Gnd to vary considerably, probably more than just half a volt or so, even if only momentarily. This causes extremely ugly conditions for clocked logic, since it will be "guessing" what's a valid clock and what isn't.

I'd guess that this is clearly a case where an extra Vcc supply, dedicated to the LED drivers is called-for. The LED's don't really care what their supply is, since the principal thing that matters to them is the current flowing through their cathodes.

A complete system spec should be laid out before us to provide the best recommendations. Guessing as much as we have tends to produce more rubbish than useful matter.

RE