Nixie tubes displaying multiple number simultaneously
Could be the IC itself that is faulty or a wrong ground connection.

Have you tried testing each component separately?


Nixie tube alone, apply 170V on anode and connect each cathode in turn, checking each digit glow on their own.
Once this is ascertained, build a circuit on breadboard with a single driver chip. Set ABCD inputs to GND. Only the 0 digit should glow. Check all possible combinations of ABCD input. Depending on the chip, starting from 1010, all digits should blank.
If not working, change the chip.
If all working fine on the breadboard, then check the PCB for shorts or cut traces.


Notes:


Measure the current through the anode. Don't go above the rated current. Usually, 3mA for smaller tubes and 8mA for large ones.
Make sure the GND of the 5V and 170V supplies are actually connected together.