In certain cases, users may notice that Packets Rx are greater than packets Tx in WLAN/MANETs/VANETs with UDP running in the transport layer

This occurs when the WLAN ack collides or is errored, the data packet is resent.

Unlike TCP this is counted twice in the Application layer if UDP is transport protocol since UDP has no means of checking for duplicate packets.

Related article:

Why do I see more packet received than sent in UDP metrics of MANET ?