I agree with you and am guilty of this same mindset, doubting TI. There have been a few situations that were difficult for me to ferret out the conflict, thus exclusion form my scan results.
Here is how I go about finding the issue:
#1 Assume that your settings are filtering out the expected stock and TI is just doing its job.
#2 Strip all the filters out and see if the Alert was being picked up in the first place
#3 Hopefully the backtest will reveal that the alert did hit the stock as you expected. Now start adding the filers back on, one at a time. Backtest with each one.
#4 Once you find the filter that caused the stock to be excluded, test that filter alone and see if it is still excluded. If so, you found the culprit.
Trust TI because most of the problems are not with TI, but they can be found in the screw that connects your keyboard to your chair.