CALC Find/Search functions not working

I imported a large-ish (10l-odd rows) .xlsx file.

I tried FIND on a visible string & got a #VALUE# error, which means not found, if I understand correctly

So I used LEFT (which works) to create a subset of my target cell as a search key; still get a #VALUE# error in FIND.

=FIND(B2, LEFT(B2,4)), for example

The function wizard shows both elements of the function are evaluating correctly.

What’s causing this?