[Observium] "Access to outside localnet is blocked "

Hello,

From 11/30 in observium.log i started to see these messages:

"[2017/12/13 10:14:05 +0000] alerter.php(9571): get_http_request() exit with timeout. Access to outside localnet is blocked by firewall or network problems. Check proxy settings. [2017/12/13 11:33:16 +0000] discovery.php(24209): get_http_request() exit with timeout. Access to outside localnet is blocked by firewall or network problems. Check proxy settings."

what could cause that ?

Thanks