I am so glad that you are still updating this much old device. I wanted to inform you that in latest build screen is not waking up when i press home button (As my power button is broken i can only wake screen with home button) and secondly 2nd sim sometimes wont show up after a reboot. When rebooted again 2nd sim comes up. And also 2nd sim in-call audio is not working. My device is j53gxx (J500H). If you coould look up to these bugs and fix them i will be more than glad. Thanks for bringing life to our 6 year old device.
look I was also having the same problem But Fixed It. Just Follow My Steps
1. Insert Both Sim Cards and go to network setting
2. select sim 1 or sim 2 settings and under network type select 3g for one sim and other sim to 2g
3. shut down your j5 and remove the sim which is set to 2g and start the phone
4.now go to sim setting and check it must be set to 3g {not LTE Its Broken}your sim 3g sim will work you can check by making a test call
4.now shut down your phone and insert the 2g with {second sim}
5.now your both sim card will eventually work {if you don't get both sims on this boot restart but don't change any settings}
NOTE. if you want to use mobile data on other sim so you have to repeat the above mentioned steps and also set 3g for data sim and 2g for other sim