In case you haven't already got one, the data sheet for the IC is here.
https://islandlabs.eu/_media/ay-5-1202.pdf The display has all digits lit, so the multiplex clock and multiplexing must be working. Check the clock input on pin 24 and that there is no leakage in the switches, especially the reset switch as the pull ups in the ic are weak and it doesn't take much leakage to cause the pin to be stuck low, also the ic socket contacts must be clean