3819773 - Why MS Teams Concur App integration cannot auto sign in instead redirecting to concur home page?

We're using SAP Concur Teams app, however, we found if we first log into Concur via web via SSO and keep the login page open, when we input key words like "expense reports" in Teams app, it still requests that we sign into Teams.
After clicking the "sign in" option, we are redirected to the Concur home signin page. The teams app cannot remember I already signed in. 
In addition, when I signed into Concur via the Teams app, if I click any reports in Teams, I am required to sign into Concur again. I cannot be redirected to the report page.
However, if I click another report after sign in, I will be redirected to report as expected.
Why does this happen?

SAP Concur Teams app requires manual sign-in even when already logged into SAP Concur web due to separate session cookies. , KBA , CON-CA-ADM , Administration , CON-CA , Cross Applications , Problem