Connection with HA UI (desktop & app) is instable several times a day

I am quite new with HA and just configured my first HA situation. I have a Rpi 3 with HA on it. Several times a day I am unable to connect to the HA web-ui (laptop) and HA app. Some notifications i am experiencing:

  • Going to HA by browser: http://homeassistant.local:8123/lovelace/0 | Feedback on screen: not available and also in light grey below: DNS_PROBE_FINISHED_NXDOMAIN
  • Going to HA by browser: 192.168.178.100:8123 | also not working. feedback on screen: not available, response takes to long, and in light greuy below: ERR_CONNECTION_TIMED_OUT
  • cmd: ping 192.168.178.100 | inmediately response on all 4 with response time of 2ms
  • cmd: ping homeassistant.local | response: `Ping request could not find host homeassistant.local.´
  • HA app )iphone’: white screen, no message. Sometimes is gives the feedback: request timed out. NSURLErrordomain - 1001
  • cmd: arp -a looked which padress belongs to the mac adress of the Rpi and that is 192.168.178.100, as configured in the router in the static ip part.
    Also the DNS should be ok, see the picture. Picture is taken on an moment that i did have contact with HA on the Rpi.

Could you please help me having a continuous running HA?

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connect a monitor to the RPi to see what is going on during those periods.