I recently tried to use Debian Stretch in production and it didn't went well. On load(500k-700k SIP messages per day) I get a problem that at some point there was a pike of CLOSE_WAIT connections(up to 2k of CLOSE_WAIT connections) and no new connections was possible, I tried to figure out where problem is, but I didn't found anything in system or Kamailio logs, Kamailio just stopped to receive traffic via TCP, but UDP continued to work. Test environment where was no load I didn't faced such issue.