I don't see where you determine what the first file is to be processed.
You have various indicators called name, appended path, and stripped path. You seem to be jumping back and forth on creating paths, but I don't see where you initially determine what is the file. I think you have problems with misuse of local variables that lead to race conditions where you don't know what is the value in the local variable because it is and when a data value was last written to the indicator. This really manifests itself in the file name scheme. You have a local variable of appended path that determines the stripped path and name and puts them into the indicator terminals. But simulataneously, you are using local variables of stripped path and name to determine the value to put in the appended path indicator terminal.
I think you have a lot of the correct elements in there. List Folder is going to give you the list of files in the folder. I don't know how you determine what Next file is vs. Previous file. Do you want it to be alphabetical, by file date, or just whatever order that the operating system returns the files?
Once you have an array of files (from list folder) then using the integer wire to determine which of the elements you want to use is correct. But you aren't quite doing that. You are taking the Name local variable, turning that string into an array (which will have exactly one element) and using the index of element (again a local variable) to either return that name back again, or an empty string in the event that the index element is greater than zero.
Overall, you have a lot of things happening in parallel when they are really sequential processes. As a result, you are using local variables to pass data back and forth between your two case structures, but there is no control over whether the data is fresh from that loop iteration, or stale from the previous loop iteration.
Set up a flowchart as to what the sequence of steps would be and program to that. You may want to look into event structures to handle button presses for next file, previous file, and read data, so that it executes the reading and analyzing of the files, and also updates the file index either 1 higher or lower when those buttons are pressed.
