Teams Unknown User displayed in chat

[IBN]

Hello,

I have a user who received a message from an "unknown user " in teams. 

I also tried to send a message to the user on teams. But my profile is showing "Unknown User" when user received my message.

I also notice the Co-existence mood for this affected was set to Teams only.

Does anyone have an idea how to resolve this issue?

What may have been the caused?

Please i need your help. 

@Eric Marsi 

@ChristianJBergstrom

@jjrice2233

@Christopher Hoard

@Allen Xu_MSFT

@Satish2805

@Steven Collier

@Ashok_Boinpally

@paul keijzers

@Bryan Nyce

@adam deltinger 

@Chris Webb

@paul1502

@Graham Walsh

@JimmyYang-MSFT

Zhengqi Lou-MSFT

Vasil Michev

Nate Loback

Yuki Sun-MSFT

[#2]

Can you desceribe more your scenario so we can figure out what might be happening? For instance: Are you coming from a Skype for Business to Teams migrations scenario?

[#3]

The user has received a message from "unknown user " in teams.

it seems that the message is received from skype.

we need to know who has sent the message. 

I have attached screen shot provided by the user. 

@Juan Carlos González Martín 

[#4]

Thanks,
But still we don't know the scenario you have...for the screenshot it seems you are coming from an upgrade scenario from Skype to Teams that actually makes sense, so I would suggest for you:
1. Double check the global upgrade mode you hve
2. For the user with the problem check the upgrade mode is inheriting or not the global upgrade mode
3. Confirm you don't have any DNSs pointing to a Skype for Business deployment

[#5]

Thanks., I will reach out to user today.
Will keep you posted about the issue