May just look like a solder ball on R17... the groove in the resistor 'case' just amplifies this perspective.

At any rate, if the wiring to HF is good and the other drivers play, there's an open (signal path in series, such as the caps) or a short (to ground, probably after the caps) in just a few related parts (including solder joints).

If a soldering iron and associated skills are available, this should be straightforward to address (pull one leg of a suspect part that's going to ground, or bypass/jumper a series connection... and use very low volume noise as a source and perhaps insert a capacitor in-line, say 1-10uF, for more tweeter-safety).

An oscilloscope (even a very cheap USB based thing) would be nice and quick, but not everyone has such a thing handy, and there is a learning curve.

Nice speakers, and worth some effort to repair/resolve.