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Dear SCMSAC DATA,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, please let us cooperate and please don’t worry, we can work together to narrow down and resolve the situation.
It seems the Comments tag feature doesn't work in SharePoint List with contribute user and even owner of the list. May I know does if my understanding is correct.
First, please accept my Apologies for the inconvenience caused to you by this behavior.
May I know does you scroll or filter to access a SharePoint list item and use @tags in messages?
Based on my test result, it seems that I cannot meet the same behavior as like you described above.
I just create a SharePoint online list and assign "Contribute" permission to user.
When I mentioned @ someone (user who have permission on list) the Comments tag send or work in SharePoint List. Here is screenshot for your reference.
To check your environment, if possible, could you please confirm does this behaviour happened to specific SharePoint online list? if possible, could you please try to open SharePoint online list into another browser or user In -private bowser and verify the result with me. It will help for us to narrow down your problem.
Also, if possible and if you don't mind (I humbly request please don't mind) could you please create a new SharePoint online list (for test purpose) and verify the result with me
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Waqas Muhammad