I saw this once for a 2.3 snapshot if I remember correctly, but since using the 2.4 snapshot (from the date 2.3 stable was announced, so it is basically the same build) I have no errors anymore. Actually the openhab.log is pretty clean 
I updated to 2.4.0 snapshot yesterday and still have the errors. Could be something left behind from a previous version perhaps? I’ll try wiping the cache again.
That’s what I did too … did not help. Lots of errors, karaf console not working, …
I ended up with a clean install, copied my config back and voila, everything is working as expected 
My karaf works fine though. Did you clean install everything or just openHAB?
I’m on Ubuntu server with nginx and I remebmer I spent quite some time setting it up some 18 months ago.
Just openHAB.
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Could this be connected to the same problem:
2018-06-01 14:31:01.542 [ERROR] [sistence.rrd4j.internal.RRD4jService] - Could not create rrd4j database file '/var/lib/openhab2/persistence/rrd4j/Steckdose_Waschmaschine_Strom.rrd': sync failed
?
Don’t know, but usually those errors go away after deleting the persistence file. It gets recreated after the first time a value is saved, but you will loose your old data 
But first I would check if the file has the correct user:group …
Did you ever solve this?
Running OH 2.5.1 on RPi4 (openhabian) I get the same errors. Just realized that they show up when I open VSC. In VSC i get a “problem connecting to REST API” (or similar) at the same time, so it’s most likely related…
Check #3