When I upgraded a couple of routerboards to v5.17 I found that the SNMP feature would no longer respond. Investigation showed that a default source IP address is not provided for the default community (public). (Note to MikroTik programmers ... ooops!)
This is what I found and how it is fixed. 
How to fix broken SNMP in RouterOS v5.17:
After v5.17 upgrade, there is no specified addresses for SNMP public community.
[admin@MikroTik] /snmp community> print
Flags: * - default
NAME ADDRESSES SECURITY READ-ACCESS
0 * public none yes
[admin@MikroTik] /snmp community> print detail
Flags: * - default
0 * name="public" addresses="" security=none read-access=yes write-access=no
authentication-protocol=MD5 encryption-protocol=DES authentication-password=""
encryption-password=""
[admin@MikroTik] /snmp community> set 0 addresses=0.0.0.0/0
Setting community addresses property to "0.0.0.0/0" fixes SNMP access.
[admin@MikroTik] /snmp community> print
Flags: * - default
NAME ADDRESSES SECURITY READ-ACCESS
0 * public 0.0.0.0/0 none yes
[admin@MikroTik] /snmp community> print detail
Flags: * - default
0 * name="public" addresses=0.0.0.0/0 security=none read-access=yes write-access=no
authentication-protocol=MD5 encryption-protocol=DES authentication-password=""
encryption-password=""
