There seems to be something wrong with virtual disk in OVA.
I normally download CHR in "raw disk image" format and then I convert it to vmdk myself. I don't exactly remember why, either there wasn't vmdk at the beginning at all, or there was some problem just uploading it to ESXi as bare file. I think it was the latter, it complained about wrong format or something.
I do this (adapter_type=lsilogic is only because qemu-image doesn't like pvscsi):
qemu-img.exe resize -f raw chr-6.44.3.img 128MB
qemu-img.exe convert -o adapter_type=lsilogic,subformat=monolithicFlat -f raw -O vmdk chr-6.44.3.img mikrotik-chr.vmdk
Then I upload resulting mikrotik-chr.vmdk and mikrotik-chr-flat.vmdk to ESXi (they get merged into one, at least in UI) and select it as new disk (connected to pvscsi controller). And it works great. Even resizing works. Shut the VM down, set larger disk size, start it again and it will occupy new free space. I can repeat it again and again and it still works. So in fact my initial img resizing should not even be necessary, it's a relict from the past when I think CHR supported resizing only on first start and not further, and I wanted to be sure that I will have enough space for the future.
But here's the thing, now I tried to skip the first step (qemu-img resize) and only converted MikroTik's original img to vmdk. And surprise, the resulting vmdk crashes CHR when resized, exactly as the one from OVA.