Returns "-1" a certain number of times

[kazuohprc]

Hello

I use this program to get distances on a regular basis.
At first the program works fine.
However, it returns [-1] from around 50 to 130 times,
After working normally 2-3 times
Returns [-1] all the time.

Normal value and pin status
1 pin_trig = ["pin_trig" <GPIO 24>] pin_echo = ["GPIO 25" <GPIO 25>]
2 pin_trig.getName () = [pin_trig] pin_echo.getName () = [GPIO 25]
3 pin_trig.getState () = [LOW] pin_echo.getState () = [LOW]
4 pin_trig.getPin () = [GPIO 24] pin_echo.getPin () = [GPIO 25]
5 pin_trig.getPin (). getAddress () = [24] pin_echo.getPin (). getAddress () = [25]
9 start_time: 45708706408821 end_time: 45708707102520
147 171 117

Bad behavior
1 pin_trig = ["pin_trig" <GPIO 24>] pin_echo = ["GPIO 25" <GPIO 25>]
2 pin_trig.getName () = [pin_trig] pin_echo.getName () = [GPIO 25]
3 pin_trig.getState () = [LOW] pin_echo.getState () = [LOW]
4 pin_trig.getPin () = [GPIO 24] pin_echo.getPin () = [GPIO 25]
5 pin_trig.getPin (). getAddress () = [24] pin_echo.getPin (). getAddress () = [25]
148 172 -1

After returning [-1], after post-processing such as
If you recreate the class, it will continue to return [-1].

sonic.gpio.shutdown ();
sonic.gpio.unprovisionPin (sonic.pin_echo);
sonic.gpio.unprovisionPin (sonic.pin_trig);

If you quit all the programs and run them again, it works fine.
However, it returns [-1] from around 50 to 130 times.
Is this a bug in pi4j?