TSE GMII gmii_rx_dv without data_rx_valid signal

Dear Community,

I am using the Triple Speed Ethernet IP Core with the GMII interface on a board with a Cyclone 10GX220.
The TSE MAC command register was initialised with:
0x2033 (SW Reset, Pad En, Promis En, RX En, TX En)

When I send a UDP Broadcast packet from the PC to the board, the packet is

visible on the GMII RX lines coming from PHY (see figure below). But data do not (or only sporadically) arrive on the Avalon-ST RX bus (see illustration) .

What could be the reason for this?

Fig.

I have connected the TSE mac according to this illustration.
The lan used has 1000Mbps.

In the rare cases where the data received via GMII arrives on the Avalon-ST RX bus, it looks like this: 

This is it should always look like!