• If the module includes flow control but it is not being used, make sure the request signals are not currently driven High. s_axi_nfc_tx_tvalid and ufc_tx_req are active-High: if they are High, s_axi_tx_tready stays Low because the channel is allocated for flow control.
• If the module includes USER-K blocks but they are not being used, make sure the s_axi_user_k_tx_tvalid is not driven High. If it is High, s_axi_tx_tready stays Low as channel is allocated for USER-K Blocks.
• If NFC is enabled, make sure the design on the other side of the channel did not send an NFC XOFF message. This cuts off the channel for normal data until the other side sends an NFC XON message to turn the flow on again.