NetSockets, server not sending all data?

Question

C++ / C#

Goodnight. I ran into a problem on a server written on the NetSockets library.
The server almost always sends not all the data.
There are 4 functions that send information to 1 or all users, but usually a couple of "packets" of data are not sent.
No errors from the server side, absolutely. What could be the problem?
I also made 2 new functions for sending data, which stop the thread for 250 ms. after sending the data.
I don't know if this is important or not: the class from where the data is sent (packed) is static.
Also, when receiving data, the server is blocked (lock (server)) so that the data is processed in turn, and not in discord.

What am I doing wrong? :(
ps- I use VPS, not locally (and locally it also loses data)