I see these errors (in red in the image):

Does anyone know what these might be?

NOTE: SmarterMail still appears to be working properly...

I'll add more details here:

ago 03 16:38:52 sm-DOMAIN MailService[841]: Microsoft.AspNetCore.Server.Kestrel[0] Unhandled exception while processing 0HNNHDIKERHAP. System.NullReferenceException: Object reference not set to an instance of an object.    at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.ServerOptionsCallback(SslStream sslStream, SslClientHelloInfo clientHelloInfo, Object state, CancellationToken cancellationToken)    at System.Net.Security.SslStream.ReceiveHandshakeFrameAsync[TIOAdapter](CancellationToken cancellationToken)    at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](Boolean receiveFirst, Byte[] reAuthenticationData, CancellationToken cancellationToken)    at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.OnConnectionAsync(ConnectionContext context)    at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.KestrelConnection`1.ExecuteAsync()

ago 03 16:38:53 sm-DOMAIN MailService[841]: Microsoft.AspNetCore.Server.Kestrel[0] Unhandled exception while processing 0HNNHDIKERHAR. System.NullReferenceException: Object reference not set to an instance of an object.    at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.ServerOptionsCallback(SslStream sslStream, SslClientHelloInfo clientHelloInfo, Object state, CancellationToken cancellationToken)    at System.Net.Security.SslStream.ReceiveHandshakeFrameAsync[TIOAdapter](CancellationToken cancellationToken)    at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](Boolean receiveFirst, Byte[] reAuthenticationData, CancellationToken cancellationToken)    at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware.OnConnectionAsync(ConnectionContext context)    at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.KestrelConnection`1.ExecuteAsync()