Bootloader or bootstack. What were you on before? If you were on Oreo you’d have to downgrade to a Nougat bootstack, like B32 or B35 maybe. Someone I know tried to do a Nougat ROM after having been on Oreo. Also got stuck like that. I wound up having to fastboot flash stock Nougat firmware to fix things up.
If you were already on Nougat then I’m not sure why it gets stuck. Maybe do a clean clean wipe by also wiping internal storage. That would require backing up a bunch of stuff first though or lose a lot of files. In lieu of that you could remove the /sdcard/Android/ directory which may hold cruft from previous ROMs. Only had to do that once or twice over the years.
You didn’t specify if you were on Oreo or not. If you were on Oreo then just flashing B32 bootstack probably wouldn’t work.
For the other user’s phone I had to fix in that case, I used Axon 7 Toolkit to flash a B32 EDL stock firmware (back to stock essentially) before being able to flash Nougat custom ROMs.
Sorry for late reply. Yep, that’s Oreo. You might have to go back to stock Nougat firmware first to be able to flash /e/ or any other Nougat ROM. You’ll have to weigh the pros and cons of going through all that just for /e/. I would say wait for /e/ Oreo but I don’t see that on the horizon. There is Lineage for microG Oreo as an alternative.