W5300 UDP packet loss (RTP receive)

I am using W5300 chip with FPGA. I use a 16 bit data bus. The bus read/write frequency is 8 MHz. The size of the receiving buffer is set to maximum. Packets are received by interrupt. The system is used to receive RTP packets from the network through the specified port. At a speed of more than 800-900 kbps, UDP packets begin to be lost. At 2 Mbps, half the packets are lost. And mostly short packets are lost. Less than 500 bytes long.