The modbus driver in advancedHMI does not support floating point, so that's the problem you're running into. sounds like you've got everything else working though.
As a workaround what I've done to display floating point numbers, like the temperature DF value of 72.5, I multiple that register by 10 in the plc and put the result in an integer register (DS), so that integer register ends up being 725.
Then in AdvancedHMI with a digital panel meter I'll read that integer, and in the meter properties you can scroll down and find "decimal location", change it to 1 and it'll put a decimal one digit in so you end up displaying 72.5 : )
You can multiply by 100 or 1000 and move the decimal place accordingly for as much accuracy as you need. If you apply all of this but in reverse it should also work great for writing to DF registers
Hope that helps! I was kind of bummed about not being able to read floating point but then realized I can display all the decimal point accuracy I need by doing the above