can’t switch language

Hello,

i have the following problems sometimes, sometimes not.

The default language is german. the problem appears, that the homepage starts in english and i am not able to switch the language.

default: https://rostocker.taxi/
en-version: https://rostocker.taxi/en/

today the page starts https://rostocker.taxi/en/ and i am not able to switch the language. I tried to deactivate the browser language detection, but it doesn’t solve the problem.
Furthermore i tried Mozilla Browser, but the problem was also with Mozilla.

I need help to solve this problem, it appears over 6 Months always for a few days.

Regards
Colin