You may have to consider the possibility that relayd is not fully compatible with your device hardware.
I personally don't use OpenWrt relayd for wireless bridging tasks because it is slow on 'lesser' hardware. My favourite is Padavan firmware. I currently use it on AC1200 MT7621 based Xiaomi 4A gigabit and Asus RT-AC57u v1 (only sold in EU) for wireless bridging.
Wireless bridging in FreshTomato is good too but number of supported Broadcom AC routers is very limited, expensive, and they run hot - I still use a Netgear R6250 for adhoc wireless bridge with a external fan attached the back.