How to debug DAQ VIs (problem with data)

Question

I am trying to debug (and understand) the attached VI.  I’m not asking anyone to analyze/debug it, since it is far more than an example; I am new to these forums and feel like asking such a thing would be inappropriate.
I would like advice on how to debug it.  I am also going to describe my problem to see if the cause may be obvious to someone.
The outputs of the "Angle Calc" sub-vi are fed into a state machine.  The state machine actuates outputs to move a motor and measures changing angles.  It first moves up/down, then left/right.  The attached VI is called by a top-level VI and the front panel is not usually open.  For some reason, when the front panel is opened, it behaves differently when it is called.  The behavior only changes for the right/left movements.
Here's where I'm hoping someone can point out some better debugging methods for me.
I have been using the Express Write to LVM File VI and the Convert to Dynamic Data function to write acquired data to text files for analysis after the acquisition has completed.  Are there better methods recommended for doing this?  I wish I could run through the code while recording the execution and then step through a playback of it!
 As for the specific problem I am having...
In the "Right Find Stall" case, the signal wired from the "Angle Calc" VI (array size 100) is connected to a Max/Min Array function.  When I log the data coming from the Min/Max function, I see an alternation between valid data and 0 (i.e. 12.2, 0, 13.3, 0, 14.0, 0, 14.5, 0...).  When I log the data being fed into the Min/Max function I do not see 0s. 
A guess of mine is that the array is empty and therefore no data is logged but Min/Max returns a 0 (not sure why this would happen).  I also have no idea why this would ALWAYS happen with the front panel opened.  I have seen the effect with the front panel closed, but never to the same degree; usually just a seemingly random zero or two but not a pattern of every other point...
Thanks all,
Dave
Attachments:
Functional_Test.vi ‏2710 KB

Answer 1

Angle_calc receives array controls in and passes array indicators out.  It performs a trig function and a bit of multiplication. 
I'll check out the Write to Spreadsheet File VI, haven't used it in the past.  If it will allow me to write text out that'll be enough reason for me to stop using the Express VI.
I've used Execution Highlighting and stepping before but with the data acquisition by the time the application makes it around to the next read the DAQ card has sampled a ton of data and the data coming in is no longer useful (a different state should be active by then).
I do think the problem is related to the computer slowing down with the front panel open.  I've logged the 'backlog' number of the Read function and found that the number in there is greater than 0 much more often when the VI's front panel is open and that I've seen relations between the 0s that I discussed earlier and the backlog going above 0 (usually the scan after a non-0 backlog seems to be a problem).
I need to familiarize myself with the DAQ basics, the buffer, backlog, and relation to sampling rate, etc.
In a simple VI I just wrote, I noticed that if I increased the sampling rate high enough, data being acquired into a chart cuts-out on a regular basis; instead of a smooth line, I see small dashes or dots of data (spaces in between).  I don't understand this- I would expect data to be lost but not "no data" to be read in.  I think understanding what is happening here would be helpful.