IP range connected to my server suddenly times out

Question

I've been leasing several /24 subnets from an external source and then I had my hosting company route them to my server.

I've added the IPs using a network-script file ifcfg-eth0-range1 with contents

IPADDR_START=xxx.xxx.xxx.2
IPADDR_END=xxx.xxx.xxx.254
CLONENUM_START=255

For several months this has been working flawlessly but suddenly I only get timeouts on one /24 subnet, all others are still working fine.

How can I find out where issue is? How can I check if it's my server, the hosting company or the 3rd party that leased the IPs to me?

Traceroute gives normally:

 10   140 ms   141 ms   145 ms  hosting.com [yyy.yyy.yyy]
 11   140 ms   139 ms   139 ms  xxx.xxx.xxx.2

Trace complete.

With the non working subnet:

 10   268 ms   279 ms   303 ms  hosting.com [yyy.yyy.yyy]
 11     *        *        *     Request timed out.
 12     *        *        *     Request timed out.
 13     *        *        *     Request timed out.
 14     *        *        *     Request timed out.
 15     *        *        *     Request timed out.
 16     *        *        *     Request timed out.
 17     *        *        *     Request timed out.
 18     *        *        *     Request timed out.
 19     *        *        *     Request timed out.
 20     *        *        *     Request timed out.
 21     *        *        *     Request timed out.
 22     *        *        *     Request timed out.
 23     *        *        *     Request timed out.