Well, I am glad that we figured out one of the two. 
As for flapping: That one’s tricky, as it can have many different reasons.
It might be that the device is just slow: SNMP Service Alert: Check_MK flapping
—> Increase check interval to e.g. 5 minutes, see if the problem persists (read more here: Monitoring via SNMP - Monitoring of SNMP devices with Checkmk)
You might be reaching the limits of what the RAW can do (unlikely): CheckMK Raw Host & Service Check Timeouts - #4 by rprengel
or about 17 other reasons…
I would start with the check interval and retries and see if that fixes things.