MashupException.Error while trying to load incremental data by DateTime field

I am currently trying to follow the suggested approach here: https://learn.microsoft.com/en-us/fabric/data-factory/tutorial-setup-incremental-refresh-with-dataflows-gen2 

I did an intial load to my table, which now contains ~ 600 records; I set up another Dataflow Gen 2, as you can see in this screenshot:

In this first step, I calculate the value I want to use as "watermark", and since I do not have a constantly-incrementing-integer-ID, I opt to use a Date-Time column "CLVLMDATE";

As you can see, I get a value back in the preview - that's good.

I also get data back, in the step 2, which actually uses the output-value from before - that's also good

Using the "Append" method, I then "Publish" my Dataflow Gen2.

But then, I get this error result:

I suspect, that there is some syntactical issue when the Dataflow Steps are combined in that Mashup Syntax?

Maybe there is some CAST, or CONVERT which I could introduce, so the Dataflow executes successfully in the end?

Can somebody elaborate a little bit on that Mashup? I guess this has to do with combining different data locations, i.e. here this would be my on-premise-oracle-database and my lakehouse.

Isn't it unfortunate, that in the power query assistant preview, everything seems to run perfectly, but when published the dataflow runs in an error?

Here I have put in the error message in plain-text for your viewing convenience.

HALL_BI_CUSLOADPROFILEVALUES: Error Code: Mashup Exception Expression Error, Error Details: Couldn't refresh the entity because of an issue with the mashup document MashupException.Error: Fehler beim Einfügen einer Tabelle., InnerException: Der Operator "<" kann nicht auf die Typen "Table" und "DateTime" angewendet werden., Zugrunde liegender Fehler: Der Operator "<" kann nicht auf die Typen "Table" und "DateTime" angewendet werden. Details: Reason = Expression.Error;Message = Der Operator "<" kann nicht auf die Typen "Table" und "DateTime" angewendet werden.;Detail = [Operator = "<", Left = error "Microsoft.Mashup.Engine1.Runtime.ValueException: [Expression.Error] Es wurde kein Wert angegeben.#(cr)#(lf) bei Microsoft.Mashup.Engine1.Language.ValueCreator.CreateValueForThrow(IThrowExpression throwExpr)#(cr)#(lf) bei Microsoft.Mashup.Engine1.Language.ValueCreator.<>c__DisplayClass23_0.<CreateValueForRecord>b__0(Int32 index)#(cr)#(lf) bei Microsoft.Mashup.Engine1.Runtime.RecordValue.DemandRecordValue.get_Item(Int32 index)#(cr)#(lf) bei Microsoft.Data.Mashup.ProviderCommon.MashupResource.TryGetValue(Func`1 getValue, IValue& value, String& errorMessage)#(cr)#(lf)Record", Right = #datetime(2006, 2, 21, 10, 1, 9)];Message.Format = Der Operator "#{0}" kann nicht auf die Typen "#{1}" und "#{2}" angewendet werden.;Message.Parameters = {"<", "Table", "DateTime"};Microsoft.Data.Mashup.Error.Context = User GatewayObjectId: 8337=========459a2e (Request ID: f92=========a87).