Replying to emails from M365 Outlook group

A problem I am stumped with, so I am reaching out for some help/guidance.

One group wants to not have the emails going into their own inbox but manage and reply only from the group inbox itself (so they know the email has been processed by deleting it once replied).

It worked OK to begin with and then some users couldn't reply, then more. Some still can. I have tried reindexing local copy, using browser instead of app & changing the send on behalf of permissions. Owner or member of group doesn't seem to make a difference.

Error messages include "This message can't be sent because it no longer exists. It can only be discarded. Make sure you copy the contents of the message before you discard if you want to use them later." and "Couldn't send this message".

Please see screenshots attached.

My questions:

1: Is Outlook on M365 designed to allow users to reply from the group either as the "group" or as themselves? Information I found isn't clear.

2: If it is / can be - what can I do to make it work for all users?

Thanks!