onnxruntime-web bug : 'return f4' is fast as normal, but 'return f1,f2,f3,f4' is very slow in webgl mode

(1)slow when return f1,f2,f3,f4
def forward(self, x):
f1 = self.b1(x)
f2 = self.b2(f1)
f3 = self.b3(f2)
f4 = self.b4(f3)
return f1,f2,f3,f4
when I return f1,f2,f3,f4 ， the onnx used in chrome is very slow. (ort.min.js using webgl)

(2) fast when return f4
def forward(self, x):
f1 = self.b1(x)
f2 = self.b2(f1)
f3 = self.b3(f2)
f4 = self.b4(f3)
return f4
when I only return f4 ， the onnx used in chrome is very fast. (ort.min.js using webgl)
but in normal , the two way should be the same time
I also find that
def forward(self, x):
f1 = self.b1(x)
f2 = self.b2(f1)
return f2
is faster than
def forward(self, x):
f1 = self.b1(x)
return f1
So anyone can tell me why?