nested interrupts for 2 uarts inputs

Hi im using 

Board: Tiva™ C Series TM4C1294

EK-TM4C1294XL

my program is listening to 2 uarts ports(uart  3 and 7)

I encounter of problem that im loosing some bytes received and im suspecting that this issue relate to the uarts interrupts.

i understand that uarts have nested interrupts but does both of them are serial?

for example: im inside uart 3 interrupt function and then while uart 3 didnt finish the interrupt(just copy their bytes to buffer) uart 7 interrupts arrives, does the system moves to uart 7 or it will first finish uart 3 and then moves to the uart 7?

currently im suffering from error bytes something like 45-400 bytes for file that his size in 12 Mbytes

im suspecting the above issue cause this issues

p.s if only 1 uart is sending data i have binary same files on both host and pc 

Thanks 

Idan