Content fallback doesn't work as expected - typo3

Question

We're developing a website for a customer which is operating all over the world. So we have 72 website languages in TYPO3 (0 = en_CH, 1 = de_CH, 2 = de_DE ...), but there are only 5 "real" languages (EN, DE, FR, ES, JA).
We want it to make as easy as possible for our customer to maintain the content so we work a lot with the "Insert records" content element and "Show content from page" pages. This works fine for normal content elements. But of course not with Extbase records which we want also have only one time in a real language.
So we tried to set config.sys_language_mode = content_fallback;1,0 as example for all german website versions (de_CH, de_DE). We also have the fallback settings in the sites config. Of course the Extbase records are all translated already in the 5 real languages.
Screenshot from the Backend
Typoscript
Swiss - German
[siteLanguage("languageId") == '1']
config {
htmlTag_setParams = lang="de-CH"
language = de
locale_all = de_CH
sys_language_uid = 1
sys_language_overlay = 1
}
[global]
Germany - German
[siteLanguage("languageId") == '2']
config {
htmlTag_setParams = lang="de-DE"
language = de
locale_all = de_DE
sys_language_uid = 2
sys_language_mode = content_fallback;1,0
sys_language_overlay = 1
}
[global]
Sites configuration
-
title: 'Switzerland (CH), German (Default)'
enabled: true
languageId: '1'
base: /ch-de/
typo3Language: de
locale: de_CH
iso-639-1: de
navigationTitle: ''
hreflang: de-CH
direction: ''
fallbackType: fallback
fallbacks: '0'
flag: ch
-
title: 'Germany (DE), German'
enabled: true
languageId: '2'
base: /de-de/
typo3Language: de
locale: de_DE
iso-639-1: de
navigationTitle: ''
hreflang: de-DE
direction: ''
fallbackType: fallback
fallbacks: '1,0'
flag: de
I expect that with these settings, the fallback should work but the output is always in english (0 = en_CH). We have TYPO3 9.5.8 installed.
You can reproduce the problem with the second link. There should be the same content as you see with the first link.
https://www.jakob.com/ch-de/produkte
https://www.jakob.com/de-de/produkte
EDIT: You can't reproduce the problem right now with these 2 links.
EDIT: This might be a problem related to this bug (marked as solved but see below).
https://forge.typo3.org/issues/86762
In the comments, some people still have the problem.
https://forge.typo3.org/issues/86762#note-40
https://forge.typo3.org/issues/86762#note-55
If you need more informations, please tell me.
Any help is very welcome!