Currently EF Core 5.0 references v2.0.1 of Microsoft.Data.SqlClient that can cause some issues we recently addressed in v2.1.0:
Release Notes

Most important issues for EF users that were solved with v2.1.0:

• Microsoft.Data.SqlClient.SNI.pdb files present in Native SNI runtime NuGet packages, that are now removed.
  Microsoft.Data.SqlClient.SNI.pdb not found with V2.0.0 SqlClient#652 (comment) - fixed by Update SNI to latest v2.1.1 for fixing pdb issues in .NET Core SqlClient#764
• InvalidOperationException and NotSupportedException errors due to WriteAsync collisions (important fix as impact was high) InvalidOperationException when writing a lot of packets asynchronously and using managed SNI implementation SqlClient#786 (comment) - fixed by Fixes "InvalidOperationException" errors by performing async operations in SemaphoreSlim SqlClient#796

and many more bug fixes :)

Please update dependency on Microsoft.Data.SqlCLient to v2.1.0 when appropriate.