Constraints validation fails

I tried out the constraints with the condition that the number of particles should be greater than zero.

...

//c1: CONSTRAINT, EXPR="numParticles > 0";
   
//objs: OBJECTIVES=(dpeak1,dpeak2,dpeak3_5);
//constrs: CONSTRAINTS = (c1);
//opt: OPTIMIZE, OBJECTIVES = objs, DVARS = dvars, CONSTRAINTS = constrs;

...

This is a dummy constraint since in our simulation we lose no particles. 'numParticles' is part of the SDDS file, i.e. *.stat file (OPAL 1.6). For some reason -- I do not understand -- I get following message in opt.trace.0:

invalid individual, constraint "c1" failed to yield true; result: 0

OPT-Pilot never finds a solution. Without the constraint, it works fine. The template and data file attached:

Ring.tmpl

Ring.data

Best, Matthias 🐛