Dropped bytes on USB COM port

I am trying to transfer large amounts of data between MKRZERO and host PC but am having reliability
problems where I eventually see 1 or 2 bytes dropped. In other words I'm transferring, say 32 bytes from
MKRZERO to PC and it works hundreds of times in a row and then one time only 30 or 31 bytes arrives. I've verified my code is at least calling the Serial.write() for all 32 bytes but the PC eventually times out.

Has anybody else had this problem?

Okay I have resolved this. For some reason when I brought up Arduino IDE it was set to "Arudino/Genuino
MKR1000" instead of MKRZERO. When I set it to the right board type I no longer get dropped bytes. Not sure
how it got set to the wrong board but it ended up being a good diagnostic lesson.