CF7 sends messages with place holders instead of content

Hi all,

we are having a strange problem: When we are receicing mails via our webpage from the contact form 7 request form, the messages appear different in our mail program.
Many times everything is sent correctly, with all the content that the sender has to enter (otherwise it will not be send as there are several required fields).
Then again we receive message only with name and surname and the email adress, and all other information fields are sent with the place holder braces, e.g. [country] [phone number] [date of arrival]
instead of the entered content.
We tried with different computers, different browsers and different smartphone browers. Any idea what else we can do?

Here is the link to our form:
https://www.hotel-pinzger.at/anfrage/

Thanks already in advance for your support,
regards,
Judith

https://www.ads-software.com/plugins/contact-form-7/