If the end hosts are not able to ping the l3 gateway and the configuration is correct then you can follow the below approach for troubleshooting:
1. Check if the mac address of the host is properly learned on the leaf switches.
2. Check for the arp entry of the host on the spine devices.
3. If arp entry is not there on the spine then try to ping from the host towards the l3 gateway and do a monitor traffic on the corresponding irb interface to check if the arp request is received on the spines and proper arp replies are sent.
4. Try clearing the arp on the host as well as on the spines.
Check for the following knobs
Hope this helps