Sorry one vertex of edge is losted

hi guys,
i am trying to import a mesh in freefem but for producing the finite elements space and setting periodic boundaries i get every time the following error:

“sorry one vertex of edge is losted”

i tried to reduce the size of elements on the boundaries but still i am getting the error. my code is as follows:
‘’’
load “gmsh”
//reading the mesh file

mesh Th = readmesh(“El_30_2D.mesh”);

//ploting the mesh to control it

plot(Th, wait=1, cmm = “Finite elemente sapace”);

//FE Space

fespace Vh(Th, P2, periodic = [[6, x], [490, x], [14, x], [482, x], [22, x], [474, x], [30, x], [466, x], [38, x], [458, x], [46, x], [450, x], [54, x], [442, x], [62, x], [434, x], [70, x], [426, x], [78, x], [418, x], [86, x], [410, x], [94, x], [402, x], [102, x], [394, x], [110, x], [386, x], [118, x], [378, x], [126, x], [370, x], [134, x], [362, x], [142, x], [354, x], [150, x], [346, x], [158, x], [338, x], [166, x], [330, x], [174, x], [322, x], [182, x], [314, x], [190, x], [306, x], [198, x], [298, x], [206, x], [290, x], [214, x], [282, x], [222, x], [274, x], [230, x], [266, x], [238, x], [258, x], [246, x], [250, x]]);

Vh u, v, u0;
‘’’

I would be grateful, if anyone can help me.
Best regards