I don’t know how many files there are usually but that’s how rrdcached looks like here:
OMD[office]:~$ ls -la var/rrdcached/
total 8
drwxr-xr-x 2 office office 4096 May 3 18:25 ./
drwxr-xr-x 14 office office 4096 Apr 23 15:03 ../
-rw-r--r-- 1 office office 0 May 3 15:03 rrd.journal.1588511037.961790
-rw-r--r-- 1 office office 0 May 3 17:03 rrd.journal.1588518237.961772
-rw-r----- 1 office office 0 May 3 17:55 rrd.journal.1588521351.653959
-rw-r--r-- 1 office office 0 May 3 18:25 rrd.journal.1588523102.796071
They are all 0 bytes tho.
No biggie I am German myself 
anyhow, if that’s the issue I could as a workaround put your solution in a cronjob. But I am unsure if that helps because the directory doesn’t look so dramatic.
For now I stopped npcd and scheduled the service. Since then the system load is at
load average: 0.09, 0.03, 0.02
Of course that’s certainly no solution but it shows that it has something to do with npcd.