Execution timeout exception in ASP.NET core

My problem is a quite hard to define. We have an SQL Server (version 15.0.2104.1) stored procedure that fills out our web site home page with data. When executed from SSMS it takes abount 0.5 second to finish. Our web site uses ASP.NET Core (Entity Framework) to execute it. Now, the strange part - after creating the procedure it runs fine on our web site. But after a while (a few hours) it starts to get timeout exceptions, while still it runs fine from SSMS. If I only resubmit the procedure code (ALTER PROCEDURE) without changing anything in it, the procedures works fine again on our web site. Then after a few hours the problem returens. I have no clue to what cause it, and since I can not reproduce it on SSMS I have no tools to correct it. Thanks.