Hap mini: no related RPC reply while installing 19.07.03

Model: RB931-2nD.

following this guide: https://openwrt.org/toh/mikrotik/common

Tiny PXE loads the temporary image all fine, Luci is reachable from port 2 via default gateway. Going system and uploading sysupgrade.bin either gets stuck on verifying image or no related RPC reply.

Repeating the same proccess with 18.06.08 results in either stuck on firmware upload image at 100% or corrupt luci

edit: restoring to stock firmware with netinstall and attempting again does not help

What could be the problem?