My Galaxy S8 was doing the same thing. Was due for an upgrade and got a brand new S10+. Message+ app saying messages are sending and they actually send sometimes and other times don't. I have messages that all pop in at once also. I am also getting disconnects during conversations on Wireless everywhere I go. Please help. Called Verizon customer service they text messaged me and said I wasn't set up for texting. Still happening. Ugh.. driving me crazy!!!