No app connection on wifi

On my Samsung Phoenix the Homey App does not wrok when I am connected to wifi. Not at home and not at work. Wen connected to 4g only, the Homey app works perfect.
However, when being on wifi or 4g, the Homey notifications always work.

On an iPhone everything is normal. No connection problems.

I have rebooted everything at home. Homey, wifi, internet and my phone.
Also remover and reinstalled the Homey app.

Does anybody know what to try next?

Why I do not know. But it is solved without doing anything.

No updates on phone and no updates on Homey since 5 days.