I'm trying to assist someone with a weird problem when using Facebook Chats from a Windows 10 Acer laptop. Often when they send a message, it disappears from their chat history BUT it stays in the recipients chat log. The recipient can reply to it but the original sent message stays gone from the senders history, it doesn't reappear when the recipient responds. Previous sender message history remains unaffected. Also if someone send them a message it will often disappear before they get a chance to read it, or it disappears shortly thereafter. I have tried clearing the cache etc to no avail. Any suggestions please?