Proxy discovery skips first address on proxy subnet, It is reproduceable every time and on different proxys. It is just the first address on the same subnet as the proxy itself that will be ignored.

Steps to reproduce:

1. Setup a remote proxy
2. Setup a device on the proxy subnet that replies on ICMP Ping. Use the first available IP address in the subnet (usually .1)
3. Configure discovery on the same subnet as the proxy. Setup the IP range to only scan the first address in the subnet (same IP as in step 2).
4. Add a ICMP Ping check

Result:
Discovery result stays empty