Using Acrobat Reader (23.006.20360) on Windows 10 but the same issue was encountered in the pro version.

The attached PDF has the word Foobar with the bar being in subscript and hence also smaller in fontsize. The second table is scaled to 70% which brings down the fontsize of "bar" to <4pt. A search for "foobar" without any quotes etc. will only bring up the one in the first table. It's broken for the one in the second table. Selecting and copy-pasting either instance of foobar works just fine.