I had this exact problem and fixed the issue by using an older version of the netinstall tool that supports BOOTP rather than just DHCP.
When I was running wireshark I noticed I was seeing bootp requests with no response. When I downgraded to netinstall 6.32
https://download.mikrotik.com/routeros/6.32.3/netinstall-6.32.3.zip
Netinstall responded to the bootp request and I could flash on the older version of RouterOS then upgrade to the latest. The setting for bootp vs dhcp is under the RouterBOARD -> Settings and make sure the Boot Protocol is set to dhcp:
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