Completely lost the ability to hear SFP internal sounds again.

Is the speaker icon on the toolbar on? It controls instant feedback on/off.

Also check if your arrangement overrides global piano and bass with one of its own instruments (Instrument menu). If so, and you removed those from the arrangement, you may need to assign again and unassign.

I'm afraid there's a bug when a 'redirected' instrument gets removed.

A reinstall would probably not help. 

If all your global instruments 'Probe' fine, they should also work for palettes and libraries, unless your library pool's sound assignment references a sound that is available (according to your global rack), but does not send MIDI to the correct output.

Step by step is difficult if we don't know the cause yet.

Open the Sound Allocation Monitor from Audio & MIDI Setup (File Menu) and look where your output goes to.

In the Library, you can assign any global sound to a pool or an entire folder of pools.

Also there's the option to use the global Piano sound for all prelistening, as a last resort (check the menu bar, standalone library only).

The embedded library uses the selected track/instrument for prelisteing, if the 'chain' switch is on. Maybe this was the case?

I have the same issue. I cant hear the internal GM synth. I did everything in this post and nothing. I even reinstalled, worked without DAW, new project, speaker icon, engine 32 and 64, everything...

I thought that the problem is related to my audio midi setup (mac os x 10.13) but I tried everything.

Please help

in aufio & midi setup, file -> new gives you a clean factory preset global rack. launch an audio engine first so plugins are used instead of the quicktime synth