When decoding the Base64 messages in the logs into a hexadecimal representation, you’re seeing the following 22 and 55 bytes packets:
7945170F26802F0001A45A84B1D1962F06FDFBD5E319
…and:
D91CE75597560C84428ACF8A7E7BB7FADA686851163FE1887C19978743582753D4B08509E7611C582D42B542390FB3C16DB6A6CDC6112B
The first byte 0x79 is binary %01111001, where the first 011 denotes an unconfirmed downlink, not an uplink. And 0xD9 is %11011001, where 110 tells you it’s reserved for future use. I guess that the error about the DevAddr is just caused by your decoder not knowing what to do.
Maybe these are random LoRa (not LoRaWAN) packets not sent by your node at all; do you see the packets at the same time your node is sending? If yes, then maybe check the antenna, and increase the distance between node and gateway to avoid distortions. If there’s any other gateway around then it would be good to see what that one receives. Also, what length of the packet do you expect?
Did the first packet even decode into something you expected? The 4 bytes after the header byte, 0x45170F26, seem to indicate it’s a TTN DevAddr, 0x260F1745, but it’s still a downlink… Due to “inverted IQ” a downlink from one gateway should not be received by other gateways, so if this is a downlink sent by another gateway, then maybe the IQ is wrong on yours?