When all settings are correct, like snmpv3 user and credentials and you still get an timeout this could happen because the number of engine boots has a negative number,
There is bug CR xos0058514 which describes an issue where the number of boots reported by snmp is negative which is impossible normally.sh snmpv3 engine-info
SNMP Engine-ID : 80:00:07:7c:03:02:04:96:36:52:90 'H'
SNMP Engine Boots : -1498960630
SNMP Engine Time : 62606
SNMP Max. Message Size : 8192
You can correct this by reconfiguring the number of boots in snmp.
configure snmpv3 engine-boots 24
The CR is fixed in below versions and higher: