Hi, did you successfully update to OpenWrt?
I have similar, but not same problem. My HW is RB951Ui-2nD (hAP). I installed OpenWrt on multiple devices in the past, but they were all 6.xx firmware.
Now I got new boxes with 7.xx firmware. They were sitting in my office, because I followed this. But in the mean time mikrotik released new firmware where boot-loop should be fixed.
So I updated to 7.20.6, but no luck. I don’t get boot loop, but after I flash sysupgrade OpenWrt image, it boots back to RouterOS. I use 25.10.5
Anyone had any luck?