I'm sorry, but I don't know why they are so far apart. One possibility is that the bromine is WAY over 10. If so, it can bleach out the color on the new strips and show as zero. Of course, it may be showing much lighter colors on pH and TA as well, if bromine IS that high. To find out if this is true, take a half-cup of water from your spa and dilute it with a half-cup of tap water. Dip. If the reading is now up on the scale, then you know you have an off-the-chart reading on the high end. If the bromine level is really high, you may have to use 1/4 cup of spa water and the rest tap.
Liquid test kits are more accurate, but I have found test strips do a good enough job to keep a spa safe and clean. If you are counting costs, the price of a liquid test kit is usually recouped. I have no idea how long it will take to do so, your mileage may vary, but it usually comes back pretty soon since you are paying a couple bucks for refill reagents instead of $15 or so for a new bottle of strips.
8-)