Question:

The 125B is responding very slow or not at all when performing Bus Health Test on modbus 485   
 

Answer:

Bus Health testing is checking if protocols have the correct level and timing of signals. Different types of communication protocols are available.
Modbus485 (also called RS-485) can be a sensitive one and can also have adjustable polling-rate.
This polling rate can be set to a time that results in the 125B taking very long time to check the levels and timings of the signal or not processing it at all.
When possible change the polling time of the signal to 125 mS. 
The 125B itself has no option to change polling time settings