ac snubber for ac relay
If the 250Vac cap in the snubber circuit gets damaged you may have problems with transient overvoltage ..
Try to add MOV in parallel with the snubber circuit .. see picture below ..
If you don't want to further experiment with DC-Relay<=>AC-Relay<=>Load configuration go for Solid-State-Relay ..
Not only it can be driven directly from MCU pin, but it switches at zero-crossing, so most of your problems should disappear ..
Regards,
IanP