Change Language on Bluetooth Keyboard

I'm using Samsung Galaxy S10 5G with Logitech K850 bluetooth keyboard with both the Android OS and the SwiftKey app updated to the latest version.

I know that Ctrl + Shift key can change between languages. The problem is, this shortcut key does not work when the screen keyboard is on. If I press Ctrl + Shift while the screen keyboard is on, the language on the screen keyboard changes, but the actual input does not change.

Instead, it shows very awkward behavior.

1. While the screen is ON, the input language by Bluetooth keyboard changes, but the input by touching the screen does change. I type by touching the screen, it exactly follows what the screen keyboard shows. But the input by Bluetooth keyboard is fixed to the one just before I turn on 'screen keyboard' mode.

2. If the input language just before turning on the 'screen keyboard' mode was Korean,

2-1. When the screen keyboard displays Korean keyboard, it works okay.

If I type 9 keys 'ㅎㅗㅇㄱㅣㄹㄷㅗㅇ', it shows

'ㅎ', '호', '홍' '홍ㄱ' '홍기' '홍길' '홍길ㄷ' 홍길도' '홍길동' in this order.

2-2. When the screen keyboard displays English keyboard, it show

'ㅎ' 'ㅎㅗ' 'ㅎㅗㅇ' 'ㅎㅗㅇㄱ' 'ㅎㅗㅇㄱㅣ' 'ㅎㅗㅇㄱㅣ' 'ㅎㅗㅇㄱㅣㄹ' 'ㅎㅗㅇㄱㅣㄹㄷ' ''ㅎㅗㅇㄱㅣㄹㄷㅗ' 'ㅎㅗㅇㄱㅣㄹㄷㅗㅇ'  in this order.

After typing this 9 keys, when I type 'Space', it turn into '홍길동' as desired.

But if I type 10 keys 'ㅎㅗㅇㄱㅣㄹㄷㅗㅇ3' then press space, it turns into '홍길동' by auto-correction.

If I type 5 keys 'ㄴㅏㄹㅗ3' then it does not become '나로3' or '나로3' but just remains 'ㄴㅏㄹㅗ3' which is no one wanted this results.