Hello,
I had my setup working without any issues (save the map), but today I
couldn't add any more devices, including an existing one I removed.
The recommended tests are OK:

root@kodi:/opt/observium# fping 10.0.0.4
10.0.0.4 is alive
root@kodi:/opt/observium# snmpget -v2c -c public 10.0.0.4 sysObjectID.0
SNMPv2-MIB::sysObjectID.0 = OID: NET-SNMP-MIB::netSnmpAgentOIDs.10

Adding the device returns no errors:

root@kodi:/opt/observium# ./add_device.php 10.0.0.4 public v2c 161 udp
Observium CE 0.15.6.6430
Add Device(s)

Try to add 10.0.0.4:
Trying v2c community public ...
root@kodi:/opt/observium#

I attached a debug from add_user, may be it can help to shed some light.
Any help is appreciated.

Gennadiy.