In case anyone runs into this issue, stop the web app (i.e. stop the app pool) and create a new execution:

USE [ProGet]
GO

DECLARE @RC int
DECLARE @Start_Date datetime
DECLARE @ExecutionMode_Code char(1) = 'O'
DECLARE @ExecutionRunState_Code char(1)
DECLARE @ExecutionType_Name varchar(50) = 'ProGet 2023 Feed Data Migration'
DECLARE @Execution_Configuration xml = (select Execution_Configuration from dbo.Executions where Execution_Id = <ID_OF_FAILED_EXECUTION>)
DECLARE @ScheduledTask_Id int = NULL
DECLARE @Feed_Id int = NULL
DECLARE @Connector_Id int = NULL
DECLARE @FeedReplication_Id int = NULL
DECLARE @Execution_Id int

EXECUTE @RC = [dbo].[Executions_CreateExecution] 
   @Start_Date
  ,@ExecutionMode_Code
  ,@ExecutionRunState_Code
  ,@ExecutionType_Name
  ,@Execution_Configuration
  ,@ScheduledTask_Id
  ,@Feed_Id
  ,@Connector_Id
  ,@FeedReplication_Id
  ,@Execution_Id OUTPUT
GO

I just encountered this on 2023.18. Any way to re-run this?

DEBUG: 2023-09-18 16:05:38Z - Deactivating feed...
INFO : 2023-09-18 16:05:38Z - Importing legacy data for npm (Npm) feed...
ERROR: 2023-09-18 16:06:46Z - Error importing data: Microsoft.Data.SqlClient.SqlException (0x80131904): Execution Timeout Expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
 ---> System.ComponentModel.Win32Exception (258): The wait operation timed out.
   at Microsoft.Data.SqlClient.SqlCommand.<>c.<ExecuteDbDataReaderAsync>b__209_0(Task`1 result)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location ---
   at Inedo.Data.DatabaseContext.DbResult.CreateAsync(DbCommand command, DatabaseContext context, DateTimeOffset startTime, Stopwatch stopwatch)
   at Inedo.Data.DatabaseContext.ExecuteInternalAsync(String storedProcName, GenericDbParameter[] parameters)
   at Inedo.Data.SqlServerDatabaseContext.ExecuteInternalAsync(String storedProcName, GenericDbParameter[] parameters)
   at Inedo.Data.DatabaseContext.ExecuteNonQueryAsync(String storedProcName, GenericDbParameter[] parameters)
   at Inedo.ProGet.Feeds.StandardPackageFeed`3.ImportLegacyPackageDataAsync[TOldRow](ImportLegacyPackageDataContext context, IEnumerable`1 oldRows, Func`2 importAsync, CancellationToken cancellationToken)
   at Inedo.ProGet.Feeds.Npm.NpmFeed.Inedo.ProGet.Feeds.ILegacyImportableFeed.ImportLegacyPackageDataAsync(ImportLegacyPackageDataContext context, CancellationToken cancellationToken)
   at Inedo.ProGet.Executions.MigrateFeedsForProGet23Execution.ExecuteAsync(IManualExecutionContext context)
ClientConnectionId:58ed9c81-5e72-4dd3-808a-612492ad0b86
Error Number:-2,State:0,Class:11
DEBUG: 2023-09-18 16:06:46Z - Deactivating feed...
INFO : 2023-09-18 16:06:46Z - Importing legacy data for nuget (NuGet) feed...
INFO : 2023-09-18 16:06:47Z - Migrating legacy .snupkg tables...
INFO : 2023-09-18 16:06:47Z - .snupkg migration complete.
DEBUG: 2023-09-18 16:06:47Z - Reactivating feed...
INFO : 2023-09-18 16:06:47Z - Import complete for nuget feed.