Steps to reproduce:
Upgrade server ZBX 3.4 (repository Zabbix) to ZBX4 (repository Zabbix)
Upgrade proxy (passive, psk) ZBX 3.0 (repository raspbian) to ZBX 4 (repository Zabbix)
My others agents version 3.4 and 4.0 work good.
Only my probem is the connection the proxy to server.

Result:
Log server side with PSK active:
1591:20181004:111424.157 cannot obtain data from proxy "NameProxy": connection closed during read

Log server side with PSK disabled:
1591:20181004:113244.778 proxy "NameProxy" at "NameServer" returned no host availability data: check allowed connection types and access rights
1591:20181004:113244.928 proxy "NameProxy" at "NameServer" returned no history data: check allowed connection types and access rights
1591:20181004:113245.082 proxy "NameProxy" at "NameServer" returned no discovery data: check allowed connection types and access rights
1591:20181004:113245.251 proxy "NameProxy" at "NameServer" returned no auto registration data: check allowed connection types and access rights