apinger:error feeding rrdtool - broken pipe - respawning too fast, waiting 300s

[opnsense_user12123]

Hi. Using 17.7.12 i get an error in gateway log after ever wan dhcp renew (see screenshot). this messages appears every minute.

apinger: error feeding rrdtool - broken pipe
apinger: rrdtool respawning too fast, waiting 300s

At that time i have no problems connecting the internet or the opnsense box.

i can only fix this temporarily by going to "reporting" - "settings" - "Round-Robin-Database" -> click "SAVE" - Button.

After that i clear up the gateway log files but the messages appear again after wan dhcp renew. (12 hours later)
Reinstall rrdtool doesn´t change anything. i´m using a cable modem!

Does anyone know this problem?