gistfile1.m

#import "RCTViewManager.h"
#import "MapboxGL.h"

@interface MapBoxViewManager : RCTViewManager
@end

@implementation MapBoxViewManager

- (UIView *)view
{
    MGLMapView *mapView = [[MGLMapView alloc] initWithFrame:CGRectMake(0, 0, 400, 400)
                                                accessToken:@"token"];
    
    return mapView;
}
@end

Yeah, - (UIView *)view should definitely always be called on the main thread. Are you certain that it isn't being? If you put a breakpoint in that method, what thread is it being hit on?

Thread 1, so I think it's something to do with Mapbox internally creating threads for rendering the map, but surely that shouldn't conflict with react-native? I thought that as long as initWithFrame is called on the main thread, all should be fine.