The reason is that your second function, fxn2, can return an invalid floating point value when both dividend and divisor are 0. This disables the lowpass filter, so it does not work for the rest of the data.

This is not really your fault, but a flaw of the lowpass filter indicator which should be able to deal with such situations. I've forwarded a notice to the developers and this will be fixed in the next update.

Anyway when you have a division in your script, always make sure that a division by zero can not happen.