I can see from your solver output that you are using the moving heat ACT that can be downloaded from our customer portal:
Ansys Store Moving Heat SourceV4.1 created by Ansys Inc
It appears development of the ACT was discontinued (a note in the image above reads "Supports ANSYS: 17.0, 17.1 and 17,2") so there may be problems (some minor incompatibilities) when it is used at 2023R1. By the way, as a favor to us, when you have a question about usage of features that are not natively supported in the Mechanical GUI, it would be very helpful to us if you could tell us so. Doing so saves us a lot of time. Well, maybe you weren't even aware that this feature is essentially an add-on - if so, that's certainly not your fault.
Anyway, when you download the moving heat ACT you get a document describing what it does and how to use it. In this document, I found the answer to your question about the spatial distribution of the moving heat source:
Without investigating with a model of my own making, I can't say why the heat load appears to be moving on only one direction or what workaround there might be for making it double back on itself as you seem to want it to do.
I noticed however that the output file reports a problem calling an array:
*** ERROR *** CP = 97.969 TIME= 14:15:36
Parameter LSTP needs subscripts.
This is likely related to the ACT not behaving as you want it to. If you haven't reviewed the documentation that comes with the moving heat ACT, it would be a good idea to download it and see if it gives you any indication that something in your setup is inconsistent with the way the ACT is supposed to be used.