Fit convergance with root version 34/03

Dear RooFit experts,
I am fitting signal PDF to proper time distribution from MC using RooBMixDecay, My model includes a convolution with complicated resolution model involving a dependence on the proper time.
The fit was working well with root 29/01. When moving to newer version: root 34/03, the fit does not converge any more. I attached the code (for a ToyMC case) & the canvas for the proper tiem distribution fit for both cases.
Using version 34 I noticed the following comment (which was not present in root 29):

[#1] INFO:Minization --  The following expressions have been identified as constant and will be precalculated and cached: (mean,sigma,Acc_Function)

I suspect the the convolution routine was changed in the new RooFit.
Any suggestions/comment will be appreciated
Thanks in advance
c_propertimefit_root34_03.pdf (24.3 KB)
c_propertimefit_root29_01.pdf (24.5 KB) (3.42 KB)