No change in output signal from SICK encoder
I do use their products over 15 yrs, if there is a need for an encoder it's definitely SICK, no other is more preferred by me. They are low priced VS. competitors and very quality made. I had no issues over all these years, not on piece was changed yet.
You have to carefully read the manual and ask the service if there is something that you don't understand.
Pay attention on the output type:

HTL means PNP (positive) 24V output pulses,
open collector means NPN output - both these types suffer at high frequency and long cable (capacitance)
push/pull (totem pole) this is preferred by me, it allows long cable and hi. freq. The output voltage usually is the same as supply voltage
TTL this is high speed, differential output 5V (line driver, similar to RS485)

For your encoder it is stated that is HTL/TTL and has a default/factory setting as TTL, but as you said it was programmed for HTL.
Probably you have burned it by wrong connection, lesson learned. I also have burned one (not Sick) and until now the last one. You do need to focus on it when mounting, there are many colors, don't hurry. Usually I do use a selective electronic fuse. Siemens PSE200U