I see that it has nothing to do with Python. I converted the reproducer to standalone C++ code:

```
const double b0_mass = 5279.66;
int rand = 0;
RooRealVar mass{"mass", "mass", 4.6, 6.0};
std::unique_ptr<RooDataSet> signal_mass{RooDataSet::read("data.txt", mass)};
double low1 = 5.26;
double high1 = 5.3;
double low = 4.6;
double high = 6;
for (std::size_t i = 0; i < 3; ++i) {
rand += 1;
auto suffix = [&](std::string const &s) { return s + "_" + std::to_string(rand); };
// signal fit
// crystal ball parameters
RooRealVar mu{suffix("mu").c_str(), "", b0_mass / 1000.0, low, high};
RooRealVar sigma{suffix("sigma").c_str(), "", 0.04, 0.025, 0.2};
RooRealVar alphaL{suffix("alphaL").c_str(), "", 0.2, 0.0, 5.0};
RooRealVar nL{suffix("nL").c_str(), "", 10.0, 0.0, 200.0};
RooRealVar alphaR{suffix("alphaR").c_str(), "", -0.2, -5.0, 0.0};
RooRealVar nR{suffix("nR").c_str(), "", 10.0, 0.0, 200.0};
// Core gaussian parameters
RooRealVar muG{suffix("muG").c_str(), "", b0_mass / 1000.0, low1, high1};
RooRealVar sigmaG{suffix("sigmaG").c_str(), "", 0.015, 0.0, 1};
// Fractions
RooRealVar frac{suffix("frac").c_str(), "", 0.5, 0.0, 1.0};
RooRealVar frac_CB{suffix("frac_CB").c_str(), "", 0.5, 0.0, 1.0};
RooCrystalBall CBR{suffix("CBR").c_str(), "", mass, mu, sigma, alphaR, nR, false};
RooCrystalBall CBL{suffix("CBL").c_str(), "", mass, mu, sigma, alphaL, nL, false};
RooGaussian Gau{suffix("gau").c_str(), "", mass, muG, sigmaG};
RooAddPdf sig_a{suffix("sig_a").c_str(), "", CBL, CBR, frac_CB};
RooAddPdf sig_fit{suffix("sig_fit").c_str(), "", sig_a, Gau, frac};
using namespace RooFit;
RooAbsReal::clearEvalErrorLog();
std::unique_ptr<RooFitResult> res{
sig_fit.fitTo(*signal_mass, PrintLevel(-1), PrintEvalErrors(-1), Save(), Timer(true), Optimize(0))};
res->Print();
}
```

I see that the fit result is different the first time compared to when you are calling `fitTo`

again. Probably this relates to some global state of the minimizer that is not correctly reset. I will continue to investigate that.

But probably, the problem would not occur if your fit converges well. Are you aware that RooFit reports the fit as unsuccessful? Here is the output of my C++ code:

```
[#1] INFO:DataHandling -- RooDataSet::read: reading file data.txt
[#1] INFO:DataHandling -- RooDataSet::read: read 36687 events (ignored 0 out of range events)
[#0] WARNING:InputArguments -- The parameter 'nR_1' with range [0, 200] of the RooCrystalBall 'CBR_1' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'nL_1' with range [0, 200] of the RooCrystalBall 'CBL_1' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'sigmaG_1' with range [0, 1] of the RooGaussian 'gau_1' exceeds the safe range of (0, inf). Advise to limit its range.
[#1] INFO:Minimization -- Command timer: Real time 0:00:07, CP time 7.230
[#1] INFO:Minimization -- Session timer: Real time 0:00:07, CP time 7.230
[#1] INFO:Minimization -- Command timer: Real time 0:00:00, CP time 0.750
[#1] INFO:Minimization -- Session timer: Real time 0:00:08, CP time 7.980, 2 slices
RooFitResult: minimized FCN value: -11813.7, estimated distance to minimum: 1.22137
covariance matrix quality: Full matrix, but forced positive-definite
Status : MINIMIZE=-1 HESSE=4
Floating Parameter FinalValue +/- Error
-------------------- --------------------------
alphaL_1 2.2833e-01 +/- 3.54e-03
alphaR_1 -3.2005e-01 +/- 4.15e-04
frac_1 9.9244e-01 +/- 7.78e-03
frac_CB_1 4.5868e-01 +/- 3.12e-04
muG_1 5.2600e+00 +/- 7.40e-05
mu_1 5.2793e+00 +/- 4.18e-05
nL_1 1.1021e+02 +/- 4.08e-02
nR_1 2.0154e+00 +/- 3.75e-03
sigmaG_1 9.5086e-02 +/- 2.74e-02
sigma_1 3.5422e-02 +/- 2.83e-05
[#0] WARNING:InputArguments -- The parameter 'nR_2' with range [0, 200] of the RooCrystalBall 'CBR_2' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'nL_2' with range [0, 200] of the RooCrystalBall 'CBL_2' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'sigmaG_2' with range [0, 1] of the RooGaussian 'gau_2' exceeds the safe range of (0, inf). Advise to limit its range.
[#1] INFO:Minimization -- Command timer: Real time 0:00:25, CP time 25.160
[#1] INFO:Minimization -- Session timer: Real time 0:00:25, CP time 25.160
[#1] INFO:Minimization -- Command timer: Real time 0:00:00, CP time 0.820
[#1] INFO:Minimization -- Session timer: Real time 0:00:26, CP time 25.980, 2 slices
RooFitResult: minimized FCN value: -11823.9, estimated distance to minimum: 5.39854
covariance matrix quality: Full matrix, but forced positive-definite
Status : MINIMIZE=-1 HESSE=4
Floating Parameter FinalValue +/- Error
-------------------- --------------------------
alphaL_2 2.0316e-01 +/- 1.04e-05
alphaR_2 -2.7724e-01 +/- 1.14e-02
frac_2 9.4489e-01 +/- 1.09e-02
frac_CB_2 4.6144e-01 +/- 5.14e-03
muG_2 5.2986e+00 +/- 2.58e-02
mu_2 5.2780e+00 +/- 1.10e-03
nL_2 1.1180e+02 +/- 3.00e-03
nR_2 1.9739e+00 +/- 4.43e-02
sigmaG_2 7.4775e-02 +/- 5.63e-02
sigma_2 3.1501e-02 +/- 2.58e-04
[#0] WARNING:InputArguments -- The parameter 'nR_3' with range [0, 200] of the RooCrystalBall 'CBR_3' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'nL_3' with range [0, 200] of the RooCrystalBall 'CBL_3' exceeds the safe range of (0, inf). Advise to limit its range.
[#0] WARNING:InputArguments -- The parameter 'sigmaG_3' with range [0, 1] of the RooGaussian 'gau_3' exceeds the safe range of (0, inf). Advise to limit its range.
[#1] INFO:Minimization -- Command timer: Real time 0:00:28, CP time 28.800
[#1] INFO:Minimization -- Session timer: Real time 0:00:28, CP time 28.800
[#1] INFO:Minimization -- Command timer: Real time 0:00:00, CP time 0.760
[#1] INFO:Minimization -- Session timer: Real time 0:00:29, CP time 29.560, 2 slices
RooFitResult: minimized FCN value: -11823.9, estimated distance to minimum: 5.39854
covariance matrix quality: Full matrix, but forced positive-definite
Status : MINIMIZE=-1 HESSE=4
Floating Parameter FinalValue +/- Error
-------------------- --------------------------
alphaL_3 2.0316e-01 +/- 1.04e-05
alphaR_3 -2.7724e-01 +/- 1.14e-02
frac_3 9.4489e-01 +/- 1.09e-02
frac_CB_3 4.6144e-01 +/- 5.14e-03
muG_3 5.2986e+00 +/- 2.58e-02
mu_3 5.2780e+00 +/- 1.10e-03
nL_3 1.1180e+02 +/- 3.00e-03
nR_3 1.9739e+00 +/- 4.43e-02
sigmaG_3 7.4775e-02 +/- 5.63e-02
sigma_3 3.1501e-02 +/- 2.58e-04
```

If always says `MINIMIZE=-1 HESSE=4`

, which means there was a problem. If things go well, the status codes will be zero. Probably the issue only happens if the fit doesn’t converge, and that’s why if was depending of the input data whether it can be reproduced.