One gray check WhatsApp not blocked

Hello,

1.  I know my friend has service and there is no internet issue and I'm curious to know why does his phone always show one check when a message is sent. There is no connection issues:  it will turn double check later or whenever. It never use to be like that. When he had his old phone there was no issues, since he got this new phone and new number it's been like this. No I'm not block.. 
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