To reproduce, build with assert and debug enabled:
$ meson build --werror --buildtype=debug -Dc_args='-DRTE_ENABLE_ASSERT=1 -DRTE_LIBRTE_MLX5_DEBUG' && ninja -C build

Run the app:
$ build/app/dpdk-testpmd -n 4 -a 0000:00:07.0,rxqs_min_mprq=1,mprq_en=1 -a 0000:00:08.0,rxqs_min_mprq=1,mprq_en=1 --iova-mode="va" -- -ia --txd=8192 --rxd=8192

Then send the following packet with scapy:
>>> sendp(Ether()/IP()/TCP()/Raw(load=b'X'*1460), iface = 'ens7', count = 1)

Result:

testpmd> PANIC in mprq_buf_to_pkt():
line 893        assert "pkt->ol_flags == (1ULL << 61)" failed
12: [/lib/x86_64-linux-gnu/libc.so.6(clone+0x43) [0x7f995daa3293]]
11: [/lib/x86_64-linux-gnu/libpthread.so.0(+0x9609) [0x7f995db7c609]]
10: [build-meson/app/dpdk-testpmd(eal_thread_loop+0x5e4) [0x55de625b5c1c]]
9: [build-meson/app/dpdk-testpmd(+0x21bc8e) [0x55de62129c8e]]
8: [build-meson/app/dpdk-testpmd(+0x21bb92) [0x55de62129b92]]
7: [build-meson/app/dpdk-testpmd(+0x1e9550) [0x55de620f7550]]
6: [build-meson/app/dpdk-testpmd(+0x1e8e22) [0x55de620f6e22]]
5: [build-meson/app/dpdk-testpmd(mlx5_rx_burst_mprq_vec+0x81) [0x55de63c17271]]
4: [build-meson/app/dpdk-testpmd(+0x1d090a0) [0x55de63c170a0]]
3: [build-meson/app/dpdk-testpmd(+0x1d049e7) [0x55de63c129e7]]
2: [build-meson/app/dpdk-testpmd(__rte_panic+0xee) [0x55de6257a485]]
1: [build-meson/app/dpdk-testpmd(rte_dump_stack+0x3d) [0x55de625a80fd]]
Aborted

OS: Ubuntu 20.04
NIC: ConnectX-5
MLNX_OFED: MLNX_OFED_LINUX-5.5-1.0.3.2
FW: 16.32.1010