try pinging with a longer timeout. the default is 2 seconds. If you are using the router to ping user extended ping like this
BB1#ping
Protocol [ip]:
Target IP address: 1.1.1.1
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]: <-- try 5 seconds
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
BB1#
If it works then your circuit is just too slow for normal tests to work.