I check for false weak by seeing if a progression of spines gives the expected results. With aluminum or carbon arrows, I pick point weights on each side of the one I want to use. If you shoot bare shafts with 100, 125, 145 and 200 grain points, each one should appear weaker than the previous one. And/or use different spined or length of shafts if you have that option. If you ever make a change that you think should result in a weaker shaft, like go from a 145 to a 200 grain point, and it gives a stiffer indication instead, then you should suspect a false weak.
Form errors can mask bare shaft results by giving inconsistent results, including false weak. Or, if you haven't learned to come to full draw with a good release, your test results could be invalid even if consistent because they are measuring a situation that will change in the future as your form improves.