When I send a message to a contact to on WhatsApp only one grey tick appears for a long...

When I send a message to a contact to on WhatsApp only one grey tick appears for a long period of time even when my internet connection is alright. I am able to send messages to all other contacts and two ticks appear when I send messages to other contacts. I have inquired that contact and they told they did not block me. I am not able to see their profile picture and last seen and even they are not able to see my profile picture and last seen. They told me that all of their privacy settings is set to "Everyone" and even all of my private settings is set to "Everyone". I am able to view all other contacts profile picture and last seen except that one contact. They told me that when they send messages to me only one grey tick appears. I have tried uninstalling and reinstalling WhatsApp but that didn't fix the issue. I contact WhatsApp almost daily through email for the solution of this issue but they did give the correct solution. I have been suffering from this peculiar problem from a long time. Hope you fix this issue for me this time. Thank you so much in advance.