Smart presence app not working after Samsung update?

I have smart presence app working together with Heimdall and it was working flawless last months.

But now I’m getting problems. After restart of homey, all is fine. Mobile phones are set as present.
After some minutes (3 to 5), all phones are set to offline. Homey itself has still internet connection.
I can access Homey with the andoid app. But stange: I’m only logged in via cloud, not local (each device is in same Wifi ans online).
The problems started after the andoid update from Samsung this week. It seems andoid is blocking the connection/requests from Homey (smart presence app).
Access from Homey to other local devices (Yamaha receiver, SonyTV, Camera…) is still working.

Has someone the same problem?
What could I check/Change (in Homey or Android)?

Thanks for proposals.

When logged in via cloud the WiFi on the phones was killed?
Check the WiFi sleeping modes on the phones.

No, phone is in Wifi and Homey app is started new. In that situation I can access other local IPs in Wifi/LAN from the phone. So I don’t think the phone is kicked from Wifi/router. Only Homey can’t access the phone.

The last two days I restarted Homey twice. Then it worked some time until the problem occured again.
I don’t know how I can reduce the error reasons to one of the devices (Homey, Router, Phone)…
Yesterday I rebooted the Wifi-AP, too. After that it was stable until today. Today it’s appearing some minutes after rebooting Homey.

How does smart presence app check the online state of the devices? Could it be that Samsung is blocking such request now? Perhaps it’s like a port scan.