LabVIEW not reading data correctly

I'm new to LabVIEW (using it for a subject at university) but I've coded up a short program that counts rising and falling edges of a signal (to be used with input of a quadrature encoder).
I've tested it at low frequency using the Simulate Signal block and it works fine, but as soon as I pump it up to anything above 4 Hz, it starts playing up (counting a positive edge as a negative edge). At 10 Hz, it doesn't count any edges at all. Same thing with the encoder - when we turn it very slowly the counts register fine, but turn it at even a moderate speed and it'll start missing.
Not sure what the issue is. The code is pretty simple so I'm not sure how that'd cause the problem. Here's a copy of my counter block (the true/false input tells it whether to count up or down).
Solved!
Go to Solution.
Attachments:
counter_block.vi ‏21 KB

I've editted the counter file to include time measurement and also included a test file from which I run the counter. It seems to struggle above 5 Hz. I've ran it in my actual file (which is similar to the test but also counts edges of a second signal) and get the same interval between codes, so the actual code doesn't seem to be the limiting factor here.
Attachments:
counter_block.vi ‏22 KB
test.vi ‏59 KB

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