Error since upgrading to 4.1

I am getting these errors now since I upgraded to 4.1. They happen even more when i am debugging the site in visual studio.

System.InvalidOperationException: A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
   at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Nop.Services.Catalog.ReviewTypeService.<>c__DisplayClass10_0.<GetProductReviewReviewTypeMappingsByProductReviewId>b__0() in C:\Projects\Main\NopCommerce\lifeseasons.com.4.1\Libraries\Nop.Services\Catalog\ReviewTypeService.cs:line 135
   at Nop.Core.Caching.MemoryCacheManager.Get[T](String key, Func`1 acquire, Nullable`1 cacheTime) in C:\Projects\Main\NopCommerce\lifeseasons.com.4.1\Libraries\Nop.Core\Caching\MemoryCacheManager.cs:line 152
   at Nop.Services.Catalog.ReviewTypeService.GetProductReviewReviewTypeMappingsByProductReviewId(Int32 productReviewId) in C:\Projects\Main\NopCommerce\lifeseasons.com.4.1\Libraries\Nop.Services\Catalog\ReviewTypeService.cs:line 133
   at Nop.Web.Factories.ProductModelFactory.PrepareProductReviewsModel(ProductReviewsModel model, Product product) in C:\Projects\Main\NopCommerce\lifeseasons.com.4.1\Presentation\Nop.Web\Factories\ProductModelFactory.cs:line 1440

Have you customised the solution or are you using an special plugins ?

Maybe there are tasks running in the background that are acting on the same context you are debugging

Looks like there is some issue with "ReviewTypeService.cs" class. Do you have any customization or custom plugin or any third party plugin?

Looking at that might help you.

Thanks for the responses. I have not made any customizations to the core code. It happens randomly whether the call is made from custom plugin, custom thing, or regular core nop code

Does it always happen "at Nop.Services.Catalog.ReviewTypeService", or does that change in the error message?

Do you have any long running Scheduled Tasks?

it happens in other classes as well, and there are no long running tasks. in fact, on my dev machine, i have all scheduled tasks disabled, and it still happens