I’ve re-read the docs around VirtualBox bridging, and the only thing that I think could possibly cause this (though it shouldn’t since ping is a direct address to a specific IP/mac) is to enable Promiscuous mode (as someone else mentioned).

This shouldn’t fix it in my opinion, but it may, since ICMP could be considered undirected traffic (I don’t, but I didn’t code VirtualBox).

I’ve sometimes found using trace instead of ping can sometimes work where pings would be blocked, plus trace shows exactly where it dies along the path.