Hmm. Can you get Synth Sample Player to produce sound by any other means? I’m using MIDI keyboard input as detailed in Dan Reynold’s guide elsewhere on the forum, rather than the PMP plugin, but I’m able to play notes by doing SetSoundWave on EventBeginPlay, then using the MIDI Note On outlet to do trigger SeekToTime (resets playback from 0s, otherwise SynthSamplePlayer will just play from wherever it left off), then SetPitch much like you’re doing in the screenshot, then finally Start. Note Off goes to a Stop. I haven’t got any envelope logic set up, but it maps to notes fine.
Are you sure MIDI note values are coming out of Event Data 1? If for some reason the frequency going to SetPitch is zero, or out of range, then that might explain it. The only other thing I can think of is that if you’re using a very short WAV (32btes, 64bytes, etc) to loop and pitch as you would in a module tracker, the engine might have some difficulties with that. I’ve not tested it yet.