Three Different Voltage Lines, Same Common Ground?
There's nothing inherently wrong with using power line buses.  Star wiring might not solve the problem.

Ideally, you'd use an oscilloscope to see how stable the power lines are.  But I'll assume you don't have one.

Consider centre-feeding the power lines, rather than feeding the power in at one end.  That reduces the cable runs.

Consider using fatter wires.  The volt drop in a thin wire could be too high.  Digital devices often require sudden spikes of current, so the power lines could be dipping even if the average voltage measured by a voltmeter looks good.

Consider adding capacitors - electrolytic and/or ceramic - between the power lines and ground near each board (you already seem to have a few ceramic ones on some boards only).  This could end up a bit trial-and-error.  Too little capacitance won't achieve what you want, too much will overload the power supplies on power-up causing them to shut down.