Openhabian not reachable

My openhabian-raspi is sometimes not reachable over the wlan interface. This is not allways the case. Sometimes I have to retry it a couple times (app oder browser) and suddenly it’s available again. It has a fix IP address and wlan is definitely strong enough.
How can I find out what the problem is?

The logs in openhab.log and/or events.log migth show something.

Check if this is an openhab issue or an issue of the system.

Look in thr system log /var/log/*.

And maybe try to ping the raspi from another pc and see if the system is reachable even when openhab is not reachable.

When I looked for information on pi4 , I found a lot comments in the Web, that one has to have a high focus on the power supply as weird issues may appear such as usb devices not recognized anymore, intermediate lack of network, and such. Maybe you should keep this also in mind

I checked all the log files and didn’t find any strange entry.
But stange is that if I ping the pi the first answer last about 1sec (the followings are in a expexted range)

You write you have a fixed IP address. How did you set it? Do you only seecthis IP address, or also one given by DHCP? Try ‘ip addr’ when you have connected.

Fix IP is defined in the router.