Here is what I managed to do so far, to understand the issue and find ways around it:
1 - Disable the SNMP agent for the host, then re-inventory it - OK;
2 - Disable the SNMP check using a rule = Disabled or enabled sections (SNMP): Setup | Agents | SNMP rules | Disabled or enabled sections (SNMP) - OK;
3 - Disable the Check_MK check using a rule = Disabled checks | Setup | Services | Service discovery rules | Disabled checks - OK;
All the above did the trick, it seems. Option #2 and #3 seem the fastest to resolve my issue.
The good thing is, right now, the conflicts are gone! I appreciate the help and feedback! It pointed me into the right direction. 