typing with Japanese keyboard

I'm a student of Japanese Studies and as such often need to write in Japanese script. Up until now it was very easy to only need to select the Hiragana input source and type away. When I wanted something to be in Katakana (カタカナ) as opposed to Hiragana (ひらがな) I just needed to hold in the shift button.

Now, however (all of a sudden), doing this doesn't produce katakana, but romaji (Latin script). This is quite frustrating because I relied on the quick and easy way of switching between the two.

I've tried deleting my input sources from the keyboard preference menu, and reinstalling them, as well as restarting the computer, all to no avail.

Please help.

Thank you!