Using Contacs groups in Bcc not possible

Steps to reproduce

1. Open new Mail
2. Got to An
3. Fill will Email-Adress
4. Go to Bcc
5. Fill with contacts group
6. push send button
7. --> No E-Mail is sending to Bcc

Expected behavior

I have a problem with the mail app in Nextcloud:
Sending emails via "Bcc" when entering a contact group from the Contacts app is not possible. When sending, the specified contact group is ignored and no one receives an email from it. The size of the contact group (number of email addresses it contains) is irrelevant. Contact groups with 2 or 87 entries, for example, are generally ignored. Even when saving the email as a draft, the contact group entry is not saved in "Bcc". When the draft email is opened, the address field is empty again.
If email recipients are added individually in "Bcc", the email will be sent. But that is not what the inventor intended if you want to write to a lot of people.
No problems when using contact groups in the "To" and "Cc" address fields. Contact groups can be used without any problems.
Does anyone have the same problem and perhaps a solution so that sending via "Bcc" also works with contact groups?
Reinstalling the Mail and Contacts app was not a solution.

Actual behavior

Sending emails via "Bcc" when entering a contact group from the Contacts app is not possible. When sending, the specified contact group is ignored and no one receives an email from it.

Mail app version

4.1.2

Nextcloud version

30.0.5

Mailserver or service

No response

Operating system

Ubuntu Server 24.04.1 LTS

PHP engine version

PHP 8.3

Nextcloud memory caching

No response

Web server

Apache (supported)

Database

MariaDB

Additional info

• Local Ubuntu server with classic Nextcloud installation
• Hardware: PC, mainboard ASRock IMB-193, CPU i5-6600, 32GB RAM
• Operating system: GNU/Linux 6.8.0-51, Ubuntu Server 24.04.1 LTS
• Nextcloud version: 30.0.5
• PHP version: 8.3.16
• Database: MariaDB 10.11.8
• Contacts app version: 6.1.3
• Mail app version: 4.1.2
• No abnormalities found in the logs

Reproduce the issue with Mail app 4.1.2 and Contacts app 6.1.3 by comparing a contact group in To or Cc with the same group in Bcc, including saving and reopening a draft. Trace the recipient handling from the address fields through sending and verify that Bcc groups are preserved in drafts and expanded when the message is sent.