Consultation on initial flow of stream

Hello, when I use the following code framework to solve the flow of stream ```makeup_chemical_a``` and run the system, I will encounter an error ```InfeasibleRegion: < reactor R: R101> conversion of 'chemical b' is over 100%; reaction conversion is infeasible```. It seems that the flow of ```stream chemical_b``` is insufficient, but I have passed the specification(```@M102.add_specification(run=True)```) to solve the required ```chemical_b stream``` flow (which is sufficient for the ```reactor R```). Besides, the input flow rate (```2000```) when defining the ```chemical_b stream``` (```chemical_b = bst.Stream(total_flow=2000)```) is the same as the flow rate of the ```chemical_b stream``` obtained by the ```specification(@M102.add_specification(run=True))```.

When I try to increase the input flow rate of the ```chemical_b stream``` to ```5000``` (```chemical_b = bst.Stream(total_flow=5000)```), there is no error. But in fact the ```reactor R``` only needs ```2000```, and the actual mass of ```chemical_b stream``` after operation is ```still 2000```, so could I consult you why is there above error ```InfeasibleRegion: < reactor R: R101> conversion of 'chemical b' is over 100%; reaction conversion is infeasible```? If I want to define ```chemical_b``` flow as 2000 instead of 5000 when defining the ```chemical_b stream``` (```chemical_b = bst.Stream(total_flow=2000)```) without above error, could I ask you what code I need to add?
Thanks for your help. Wish you a good day.

The process flow is as follows.

The code framework is as follows.
```
makeup_chemical a = bst.Stream(
ID=' makeup_chemical_a',
price=0.57,
total_flow=1000,
units='kg/hr',
chemical a=1,
)

chemical_b = bst.Stream(
ID=' chemical_b',
price=0.3,
total_flow=2000, # if total_flow=5000, no error reports
units='kg/hr',
chemical b=1,
)

Sugar= bst.Stream(
ID=' Sugar ',
price=0.1,
total_flow=5000,
units='kg/hr',
glucose=0.2,
xylose=0.3,
mannose=0.5,
)

recovery_chemical_a= bst.Stream(ID='recovery_chemical_a ')

M101 = units.Mixer('M101', [makeup_chemical_a, recovery_chemical_a])
Stream a = M101-0
M101.chemical_a_loading_per_dry_mass = 15
Required_mass_ chemical_a = M101.chemical_a_loading_per_dry_mass * Sugar.F_mass

@M101.add_specification()
def M101_chemical_a_spec():
makeup_chemical_a.empty()
makeup_chemical_a.imass['chemical a'] = max(0., Required_mass_ chemical_a- recovery_chemical_a.imass['chemical a'])
M101._run()

M102 =bst.Mixer('M102', [M101-0, Sugar, chemical_b])
@M102.add_specification(run=True)
def update_chemical_b_loading():
chemical_b.imass[‘chemical b’] = Required_mass_ chemical_a / 30
```