If there’s an applied V11 chord, sometimes the absolute chord is labelled as:
[Bass note]/[major chord 1 semitone below it] e.g. A/Bb
instead of
[Bass note]/[major chord 2 semitones below it] e.g. Ab/Bb
However if the V11 chord is not applied then it labels it correctly
Happens in both theorytabs and hookpad