Phone field problem

Hello,

Some (very few) people cannot send a form because of a faulty phone field
(see screenshot https://my.pcloud.com/publink/show?code=XZW2Qi7Z0k0S56GCpuHiBn5QUVFGvV4VCXMX)

What could cause this problem. I’ve tried to reproduce the issue but for me it work fine.

Thanks

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