The claim that nine House Republicans crossed party lines to advance a Democrat-led bill to extend ACA subsidies for three years is mostly false because multiple reliable sources consistently report that only four moderate House Republicans joined Democrats in this effort, not nine.
Nine House Republicans crossed party lines to advance a Democrat-led bill to extend ACA subsidies for three years.

Republicans join Democrats to force vote on healthcare subsidies
Source: bbc.com
Key Evidence
The Washington Post and The Hill both report four moderate Republicans joined Democrats to force a vote on ACA subsidy extension.
BBC names the same four Republicans who signed the discharge petition with all Democrats.
Republican Herald highlights Mike Lawler as one of these four crossing party lines. None of these sources mention nine Republicans.
What the Evidence Shows
All four sources agree that a small group of moderate Republican House members joined Democrats to force a vote on extending the Affordable Care Act (ACA) subsidies. Specifically, The Washington Post, The Hill, BBC, and Republican Herald identify four Republicans by name: Ryan Mackenzie, Rob Bresnahan, Brian Fitzpatrick (all from Pennsylvania), and Mike Lawler (from New York). These four Republicans signed a discharge petition or otherwise supported the Democrat-led effort to extend the pandemic-era enhanced ACA subsidies for three years.
None of the sources mention nine Republicans crossing party lines; instead, they emphasize the limited number of GOP moderates involved. The claim overstates the number of Republicans who crossed party lines by more than double. The context also shows this was a significant but small bipartisan move against GOP leadership preferences.
Therefore, while the core fact that some Republicans supported the bill is true, the specific number 'nine' is not supported by available evidence.