I exclusively use USB link for all my Arduinos… mainly because I have no other option at this time 
So here are my hints and tips:
AVOID all references to the same serial connection that the link utilises. That means you MUST modify many of the examples to comment out #define BLYNK_PRINT Serial and duplicate Serial.begin(9600); lines.
Do not open the IDE monitor, or any other terminal program (if on same COM port)… common sense you say?? perhaps, but sometimes I have had a minimised window that I forgot to close 
Speaking of minimised windows or forgetting… always make sure your batch script IS running, on the correct server designation (cloud or local IP), COM port and BAUD rate, as well as not showing any errors or repetitive connection attempts.
When lockup/disconnect issues happen, the best way to reconnect is to close and restart the batch file script… while I have seen it automatically reconnect at times, it is not always reliable. That said, I have had links that have lasted days, with glitches but still reconnect, eventually, particularly if I close the app (but not stop the project) then reopen the app.
Don’t attempt to do too much, or assume that a faster BAUD rate is better… basic serial communication does not have the same packet error correction as TCP/IP, so some data might get missed and cause continuity issues.