The way I fixed this -
1. Login to Azure DevOps, create a new PAT with full access .
2. Copy the token to your clipboard.
3. Login to your LCS project, select the Project settings -> Azure DevOps -> Setup Azure DevOps.
If you've already configured LCS to connect to your Azure DevOps project, you can either skip this procedure or select Change to change the existing configuration.
4.Enter the root URL for your Azure DevOps account, and the personal access token that you created earlier, and then select Continue.
5. Select your Azure DevOps project.
6. Specify the mapping between LCS/BPM items and the associated Azure DevOps work item types.
Basically a lot of clicking Next, Next, Next. No changes required in LCS, just paste the personal access token (PAT).
d365technext.blogspot.com/.../vsts-token-expire-on-lcs.html