According to your description, I have the following questions to confirm with you：
1.Does anyone else have the same problem in your organization?
2.Is the Teams working slow when you are using Teams Web client? If the web client can log in successfully, you can re-download the desktop client.
3.What version of your operating system is it? If necessary, you could update the operating system.
We recommend that you check the hardware configuration. For more details about hardware configuration requirements in Teams, you could refer to this link's table.
Besides, you could check the network bandwidth. For more details about hardware configuration requirements in Teams, you could refer to this link's table.
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I am writing to see how everything is going on with this thread. Should you need more help on this, you can feel free to post back.