I think this has something to do with this line:
midiNote = activeNotes[Random::getSystemRandom().nextInt(activeNotes.size())][0];
and activeNotes going out of bounds resulting in a segmentation fault:
JUCE Assertion failure in juce_Random.cpp:80 Segmentation fault: 11

i tried it in lmms doesn't have a gui.

have you thought of GRNLR as an lv2 plugin
http://lv2plug.in/

Investigate further...

Plugin Crashes on Windows when grains are triggered very quickly (>0.01s) due to the vector holding the grains getting out ouf bounds.

This is most likely because we iterate over the vector while we are deleting finished grains.

Add a logging mechanism to make debugging in commercial DAWs easier. Right now the Terminal Output of the Plugin is only accessible from the JUCE Plugin Host. DAWs like Logic or Ableton don't output much to the Terminal so it would be useful to write all the output to a log file!

The Message Thread is only started when the GUI of the plugin is opened. This results in the values of all the parameters and the sample path not being restored until the GUI is opened by the user.

Find some way to start the message thread at the same time the audio thread is started!

The scheduling threads doesn't wait the correct amount resulting in the grain onsets jittering. The difference between the time the grain should play and it actually playing seems to be related to the sample rate:

dur: 0.24 next: 11520 jitter: -256
dur: 0.24 next: 11520 jitter: 256
dur: 0.24 next: 11520 jitter: -256
dur: 0.24 next: 11520 jitter: 256
dur: 0.24 next: 11520 jitter: -256
dur: 0.24 next: 11520 jitter: 256

dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: 384
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: 384
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128
dur: 0.024 next: 1152 jitter: -128

a multiple of the sample rate (48khz) doesn't result in errors:

dur: 0.48 next: 23040 jitter: 0
dur: 0.48 next: 23040 jitter: 0
dur: 0.48 next: 23040 jitter: 0

It appears that the constructor for GrrnlrrAudioProcessor is called two times.

When trying to add a logging class to the project (and not deleting it in the destructor) I got this warning from JUCE:

*** Leaked objects detected: 2 instance(s) of class FileLogger
JUCE Assertion failure in juce_LeakedObjectDetector.h:95

But there should have been only one instance of FileLogger created...

Plugin Returns when closing:

*** Leaked objects detected: 1 instance(s) of class Random
JUCE Assertion failure in juce_LeakedObjectDetector.h:95

maybe fix by using getSystemRandom()

Add alt-click function to reset parameters to default