Pressing and releasing J works as expected:
/dev/input/event13: 1506.928 - 0x01/EV_KEY - 0x024/KEY_J - 1
/dev/input/event13: 1506.953 - 0x01/EV_KEY - 0x024/KEY_J - 0
/dev/input/event13: 1506.953 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

I will press and release right-shift:
/dev/input/event13: 1518.606 - 0x01/EV_KEY - 0x02a/KEY_LEFTSHIFT - 1
/dev/input/event13: 1518.632 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0
/dev/input/event13: 1518.927 - 0x01/EV_KEY - 0x02a/KEY_LEFTSHIFT - 0
/dev/input/event13: 1518.954 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

I will now press and release J again (this will input ctrl-J to any application):
/dev/input/event13: 1530.246 - 0x01/EV_KEY - 0x024/KEY_J - 1
/dev/input/event13: 1530.271 - 0x01/EV_KEY - 0x024/KEY_J - 0
/dev/input/event13: 1530.271 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

And again:
/dev/input/event13: 1538.026 - 0x01/EV_KEY - 0x024/KEY_J - 1
/dev/input/event13: 1538.052 - 0x01/EV_KEY - 0x024/KEY_J - 0
/dev/input/event13: 1538.052 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

Now I will press and release right-ctrl to reset the situation:
/dev/input/event13: 1547.044 - 0x01/EV_KEY - 0x01d/KEY_LEFTCTRL - 1
/dev/input/event13: 1547.069 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0
/dev/input/event13: 1547.259 - 0x01/EV_KEY - 0x01d/KEY_LEFTCTRL - 0
/dev/input/event13: 1547.285 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

Now J works as expected again:
/dev/input/event13: 1555.439 - 0x01/EV_KEY - 0x024/KEY_J - 1
/dev/input/event13: 1555.465 - 0x01/EV_KEY - 0x024/KEY_J - 0
/dev/input/event13: 1555.465 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0

And again:
/dev/input/event13: 1560.574 - 0x01/EV_KEY - 0x024/KEY_J - 1
/dev/input/event13: 1560.601 - 0x01/EV_KEY - 0x024/KEY_J - 0
/dev/input/event13: 1560.601 - 0x00/EV_SYN - 0x000/SYN_REPORT - 0