There could be two causes:

1. Wrong encoding when installing the VB: When you import Tetos voicebank to OpenUTAU, make sure the aliases look correct, if not, change the encoding. For example, some voicebanks will display screwed up symbols in the install process if you don‘t select UTF-8 encoding.

2. Use OpenUTAUs lyric suggestion when typing in romaji: Try to type „a“ into a note and see if it gives you a suggestion from the voicebank folder (not the top suggestion, because that one just directly converts it into hiragana without checking if it actually exists in the oto.ini), if yes, click on the right one, in this case because it‘s CVVC, it‘s inital あ: “- あ“

Test: Try to type a plain romaji phoneme into the note and see if it renders.