The ESXi 6.5 installation image contains version 1.8 of the Host Client, and the current version is 1.18. I'd suggest you either update/patch the host with the latest available patch bundle, or update at least the Host Client (see e.g. https://esxi-patches.v-front.de/ESXi-6.5.0.html for the download link).
Please note that Microsoft's Internet Explorer has a maximum size limit of 4GB when it comes to uploads, so ensure that you use another browser.
André