I have a repro for this. This F# project: https://github.com/srid/Baseline (dotnet run the Baseline.CLI project)

• Main entry point: https://github.com/srid/Baseline/blob/346ff7bdb70d131c03469e5f7d7e62b16926d581/src/Baseline.CLI/Program.fs#L12-L19
• Types: https://github.com/srid/Baseline/blob/master/src/Baseline.Data/Library.fs#L7-L56

When I run the program multiple times, each time it loads the .journal file (which seems to be created correctly) but discards the command field values in them, instead filling them with null. See terminal output:

As you can see all but the last record (which was inserted in current thread) is filled with null. All but last record was loaded from the .journal file at program startup.

The command itself looks about right:

type Think(s: string, t: DateTime) =
    inherit Command<BaselineModel, DateTime>()

    member this.Content = s
    member this.When = t
    
    override Command.Execute(model: BaselineModel): DateTime =
        let thought = model.Think(s, t)
        Command.RaiseEvent(ThoughtSaved(thought))
        thought.When

Did I hit a bug in memstate?