In theory what you want to do is very simple. You open a form instance with a subform. So the form instance is filtered to a specific record and the child records would then be filtered to a set of records. Since every instance is a filtered set no instance sees the same records. It all appears like a separate "table" but each instance is just filtered.
Now you can take my advice or leave it, but in my opinion your implementation needs to get fixed. The query you showed is ridiculous. I have seen thousands and thousands of queries, but nothing that overly complex. I would get rid of that. The 5000 record subform is a poor implementation that I would also get rid of. Not sure what that is, but I am assuming it is a temp table to hold records and used for an insert query. That is not needed and only adds complexity. Part of the problem is that you have this spaghetti code and query, that is so complex it is unusable. If you design a database that is so complex that you can no longer use it you might just have a problem. Being able to write complex code is not what makes a good programmer, being able to write clean, concise, reuseable code is.
I know a little about designing Access applications so if you do not want to listen to my advice then you can keep putting these band-aids over top other band-aids, and hopefully somehow else can help out. Unfortunately for you on this forum there are a handful of people that routinely deal with recursion and form instances. You can look up my posts and I have posted numerous threads on both topics.
If you want my help, post the form query (not an image) and let me help you redesign it. If you simplify this then everything else is simplified. As I said what you want to do is very simple, your implementation; however, is overly complex. If you want a band aid then make the subform unbounded and do an insert query. This way everything in the subform is "seperated". Or use an ADODB disconnected recordset for each subform to allow you to really add disconnected records. That should add some good additional complexity.
You may not know Rube Goldberg, but I get a sense this is what you are trying to build.