Comment 2 for bug 1662374

The system was designed to pre-allocate all group state on the main thread for groups that exist when the effect is instantiated.

It looks like this isn't working for the default effect chains because they are created before the decks/samplers/etc. are setup.
https://github.com/mixxxdj/mixxx/blob/master/src/mixxx.cpp#L189

Be: Were you using master or was this using your persistent effects branch? Since you load effects in EffectsManager::setupDefaults(), the loaded effects will also not get their group state pre-instantiated.

It should be safe to move setupDefaults() to after the decks/samplers/mics/auxiliaries are setup.